Obviously you haven't ordered yet. I meant if you look at a list of recommendations and there's 150$ headphones and 600$ headphones it's obvious which ones are going to be better. That's why you have to figure out your price range first and then compare headphones in that range. Figuring out whether or not headphones for x€ get you what you want is a different matter and you'll obviously need to test headphones for that. Recommendations at different pricepoints for that, but you were already considering buy the DT 1990 without testing any.

Which headphones did you try and which did you like best? I might be able to find something similar.

Nope, can.
Most likely you won't be able to test the exact DAC/amp/headphones combination you want to buy, but I know it's tempting when you read reviews, where all the faults, shortcomings and downsides of headphones are pointed out, to think that those aren't good enough and you should look for something better (which will usually end up being more expensive). In those cases if at all possible you should test the headphones first.

Probably not, apart from Amazon (which is usually more expensive in the first place) it doesn't really happen in Europe anyway.

If it wasn't on high the GPU wouldn't matter. That's why I asked.
More or less expected, yes, but can't hurt to check.

#2668
Remember, you wanted to make this https://uk.pcpartpicker.com/list/BXTZtJ cheaper.
Now you've gone mini ITX and it's almost 200£ more expensive, still with a cheap aio that can't beat air coolers of the same price. https://i1.wp.com/www.modders-inc.com/wp-content/uploads/image//2017/08/graph2.jpg
FYI the Mugen 5 costs half. Strap a 2000 rpm fan on it and it would win while still being cheaper and quieter.

This is going to end exactly the same like it did every time. You'll realize that you can't afford what you want and don't want what you can afford and then you'll give up and try again in a few months.

@everyone: This might sound mean but I've made too many partlists for him already.

#2669
Nah, just to make sure because it's over budget.

i5-8600K at least 315€ and that's from Czech Republic https://www.alza.de/intel-core-i5-8600k-d5116998.htm?o=1
https://geizhals.de/intel-core-i5-8600k-bx80684i58600k-a1697344.html
Cryorig H7 ~35€ https://geizhals.de/cryorig-h7-cr-h7a-a1233532.html
ASRock Z370M Pro4 ~112€ https://www.mindfactory.de/product_info.php/ASRock-Z370M-Pro4-Intel-Z370-So-1151-Dual-Channel-DDR4-mATX-Retail_1200385.html
mindfactory not listed on geizhals for some reason https://geizhals.de/asrock-z370m-pro4-90-mxb660-a0uayz-a1701182.html?hloc=at&hloc=de
2x8GB RAM ~167€ https://geizhals.de/g-skill-aegis-dimm-kit-16gb-f4-3000c16d-16gisb-a1474853.html?v=k&hloc=at&hloc=de
There are other options should that kit not be available anymore at that price.
850 Evo 500GB ~154€ https://geizhals.de/samsung-ssd-850-evo-500gb-mz-75e500b-a1194263.html
cheaper (slower) options do exist if we have to save a bit of money.
N200 ~44€ https://geizhals.de/cooler-master-n200-nse-200-kkn1-a919524.html
Mostly a placeholder, get whatever you want. There's also a version with a tiny window, if you want that, which is actually cheaper. https://geizhals.de/cooler-master-n200-nse-200-kwn1-a919657.html
550W PSU ~65€ https://www.mindfactory.de/product_info.php/550-Watt-Corsair-CX-Series-CX550-Non-Modular-80--Bronze_1157929.html
or https://geizhals.de/corsair-vengeance-550m-550w-atx-2-4-cp-9020111-de-a1405278.html?hloc=at&hloc=de
or https://geizhals.de/evga-b3-serie-550-b3-550w-atx-2-4-220-b3-0550-v2-a1654218.html?hloc=at&hloc=de
whichever is cheapest where you're buying other parts. Again mindfactory not listed for some reason so you'll have to search manuall on their site if you're going to buy it there. Of course this has to happen today. Non-modular CX550 is vastly different from the semi-modular CX550M, don't buy it just because it's cheaper.
CD/DVD ~13€, lots of options https://geizhals.de/?cat=dvdram&xf=5011_1%7E9514_DVD-Brenner#gh_filterbox

Total: ~905€

Which Ryzen 7 exactly? Overclocked?
RAM speed and timings?
Actually plugged the monitor into the GPU and not integrated graphics? Drivers installed?

850W PSU for a ~300W build. I will never understand this.

Option 2 as in #2662 option 2 = 1600(X) or as in #2665 option 2 = 8600K?
Just to make sure.

If you're investing this kind of money you should try a few headphones and figure out what you actually like instead of just guessing.
You're in a position where not only you can choose but you have to choose because no headphones are perfect.
Letting someone on the internet guess for you what you might like isn't a good idea.
Go to a store. An actual professional store that'll let you do some listening tests.

Keep in mind that DACs/amps can't magically make headphones sound better. Headphones are inherently imperfect, they'll always change the signal that goes in by a few percent, whereas for DACs/amps the goal is to get as close to zero percent as possible.
So beyond the DAC/amp not doing horrible things with the signal you feed it and in case of the amp providing enough voltage/current/gain more money only buys you features and getting closer to perfection. Of course I'm ignoring tube amps because you don't want to go down that rabbit hole. Anyway this means if you're spending more on your amp than on your headphones your priorities are probably wrong. Headphones first, DAC/amp that do their job properly are a must, beyond that only if you can afford it. It's not worth giving up headphones that suit your tastes much better just to get an amp with 0.001% lower THD+N.

Value is highly subjective for audio.
Diminishing point depends on your tastes and hearing. If you can't hear above 20kHz anymore anyway then you probably don't care about a spike at 22kHz. On the other hand if you can hear PSU noise at 25kHz and it drives you insane then you should probably pay attention to that.
Set yourself a budget. Or this will escalate really quickly.
I mean you're looking at 150$ and 600$ headphones and compare them as if the money didn't even matter. And that's all based on the guess that you really want a neutral sound signature.
After that you start worrying if the DAC/amp are really good enough if you're investing that much money. Then you start comparing the 600$ ones with other 400-600$ headphones because it's only fair, right, and there might be something even better at that price.
Stop, take a step back, set yourself a budget with max +x€ if you need an extra 20€ or something like that to make a certain headpones + DAC + amp combo happen. Then work with that. If you're really not satisfied with what that gets you can start over. But really if you can test at least the headphones before you decide that's not good enough.

v5 = v4 + modular cables + both mic options (omni/uni-directional) at the same time.
Omni-directional v4 isn't sold anymore afaik.
So for omni (or both, if you think you'll need to switch depending on the environment) or if you want modular cables v5.
Otherwise v4.
Uni-directional needs a lot of gain and I have yet to see onboard sound that could provide enough. You might be able to get away with it with the v5 set to omni-directional but I wouldn't count on it. Any cheap USB ADC is enough though.

EDIT: Once you've decided on headphones you can actually do the math how much voltage/current/gain/power the amp needs to be able to provide.

Good.

1600X doesn't include a cooler so it's kind of necessary.
i5-8400 can't be overclocked so stock cooler is usually enough. You'd need an i5-8600K or drop down to an i3-8350K, but even with the overclock you'd end up with the same performance as with the 8400 at best while streaming and only better with just TF2 so it's a sidegrade. 8600K + cooler (again, not included unlike the 8400) would be over budget. Could go with 120GB SSD + HDD to save a bit of money but I'm not sure it's worth the tradeoff.
I wouldn't worry about overclocking future processors. Unless you want to upgrade really soon (and not even then probably if it's Intel) it'll be a different socket so you need a new mobo as well and the cost for a new cooler isn't all that significant anymore and you might not have a choice anyway if the dimension of the socket are different and old coolers physically don't fit anymore.

I'm hoping you don't need a 100€ Win10 license within the same budget.

Anyway your options are:
1. i5-8400, no overclocking, stock cooler. If it doesn't reliably get the max turbo clockrates you can still buy a cooler later and stay within budget.
2. i5-8600K, overclocking, cooler. Over budget, but not that much. Probably the fastest though.
3. 1600, overclock, stock cooler. Again you can buy an aftermarket cooler later if you find out you do need one, but it runs into a wall at 4 GHz regardless of cooler so it'd only be for noise/temps. Cheapest option, beats #1 in streaming and comes close when not.
4. 1600X, overclock or none (runs into the same wall at 4 GHz which is the max turbo anyway), cooler. If you're overclocking it would perform almost the same as #3 only more expensive.

#2660
Well 250GB SSD + 1TB HDD costs almost the same as a 500GB SSD, so if 1TB is more than enough then maybe 500GB are enough and you don't need to worry about what to put where? Also you can just keep your old HDD.

Windows 8.1 I hope?
Not so much TF2 related problems with Win10, only Win10 related problems with Win10. E.g. replacing working drivers with broken ones, automatic updates, breaking full screen, breaking VSync, forcing VSync and so on.
Main problem with Win8.1 is actually that Microsoft decided since even after they announced there would be no performance updates for new CPUs on Win7/8 no one wanted Win10 it was time to take drastic measures and block all updates if you dare to use a new CPU with Win7/8. Of course there's a user-made patch that just disables the software they use for detecting offending CPUs.
The other problem would be Win8(.1) being weird in general, but most of that can be fixed with e.g. Classic Shell (except the control panel being split between metro and classic interface, only Win10 fixes that).

So here's a few options. These are by no means the final partlists because pcp is awful for Germany (outdated prices, few shops, counts shipping for every item so everything <100€ basically defaults to Amazon).
PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i5-8400 2.8GHz 6-Core Processor (€239.99 @ ARLT)
Motherboard: ASRock - Z370M Pro4 Micro ATX LGA1151 Motherboard (€113.96 @ Mindfactory)
Memory: Corsair - Vengeance LPX 16GB (2 x 8GB) DDR4-2800 Memory (€183.76 @ Amazon Deutschland)
Storage: Samsung - 850 EVO-Series 250GB 2.5" Solid State Drive (€93.98 @ Amazon Deutschland)
Storage: Seagate - BarraCuda 1TB 3.5" 7200RPM Internal Hard Drive (€41.32 @ Amazon Deutschland)
Case: Cooler Master - N200 MicroATX Mini Tower Case (€40.46 @ Amazon Deutschland)
Power Supply: Corsair - CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply (€73.13 @ Mindfactory)
Total: €786.60
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-11-22 20:19 CET+0100
Probably the fastest just for TF2, assuming it actually gets the full turbo clockrates (might have to fiddle with mobo settings because of power draw, maybe add a cooler because of the heat).

PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 5 1600X 3.6GHz 6-Core Processor (€209.00 @ Caseking)
CPU Cooler: CRYORIG - H7 49.0 CFM CPU Cooler (€34.90 @ Caseking)
Motherboard: Asus - PRIME B350M-A Micro ATX AM4 Motherboard (€76.99 @ Amazon Deutschland)
Memory: Corsair - Vengeance LPX 16GB (2 x 8GB) DDR4-2800 Memory (€183.76 @ Amazon Deutschland)
Storage: Samsung - 850 EVO-Series 250GB 2.5" Solid State Drive (€93.98 @ Amazon Deutschland)
Storage: Seagate - BarraCuda 1TB 3.5" 7200RPM Internal Hard Drive (€41.32 @ Amazon Deutschland)
Case: Cooler Master - N200 MicroATX Mini Tower Case (€40.46 @ Amazon Deutschland)
Power Supply: Corsair - CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply (€73.13 @ Mindfactory)
Total: €753.54
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-11-22 20:20 CET+0100
Cheaper, better for streaming, but slightly worse for TF2 when not streaming.
If you were willing to overclock you could get the 1600 instead of the 1600X, would end up being the same speed. 15€ isn't much but you can actually get away with using the stock cooler (1600X doesn't include one) even with an overclock so it ends up being >=50€ cheaper.

PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 7 1700 3.0GHz 8-Core Processor (€284.59 @ Alza)
CPU Cooler: CRYORIG - H7 49.0 CFM CPU Cooler (€34.90 @ Caseking)
Motherboard: Asus - PRIME B350M-A Micro ATX AM4 Motherboard (€76.99 @ Amazon Deutschland)
Memory: Corsair - Vengeance LPX 16GB (2 x 8GB) DDR4-2800 Memory (€183.76 @ Amazon Deutschland)
Storage: Samsung - 850 EVO-Series 250GB 2.5" Solid State Drive (€93.98 @ Amazon Deutschland)
Storage: Seagate - BarraCuda 1TB 3.5" 7200RPM Internal Hard Drive (€41.32 @ Amazon Deutschland)
Case: Cooler Master - N200 MicroATX Mini Tower Case (€40.46 @ Amazon Deutschland)
Power Supply: Corsair - CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply (€73.13 @ Mindfactory)
Total: €829.13
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-11-22 20:22 CET+0100
Even better for streaming, but probably overkill. Also basically requires an overclock or you'll get less fps in TF2 than with option 2 (with an OC it would be the same).

You can change your mind about SSD/HDD and overclocking or don't, then you can pick one of the three options and I'll make the final partlist.

In that case: SSD only or SSD + HDD? Size for each?

Anything you might want to reuse other than the GPU?
Focus on most fps in TF2 or streaming?
Should be doable with 800€.

#6
And now find 3 that ship to Ireland for <30€. Bonus points for correct layout unless CardfightGamer really likes the french one.

http://i.imgur.com/qMoJ0h8.jpg

#3
30€, not 30$.
Not happening including shipping.
VAT is also a thing in most countries.

#4
Check again, not £ either.
Find 3 mechanical keyboards <30€.

I just want OP to check prices and realize that unless "around 20 to 30€" means around 40€ full size linear isn't going to happen.

Are there any mechanical keyboards for 20-30€ regardless of switch type? I don't think so.