the only way to get trails back on dx8 is to either
1: Rollback drivers (which u said u wont do so this isnt going to work)
2: Get an Nvidia graphics card (not worth the money for rocket trails)
My advice is to use dx9 and use commands to make ur game look like dx8:
r_worldlights 0
mat_phong 0
mat_specular 0
mat_hdr_level 0
r_ambientboost 0
r_rimlight 0
mat_monitorgamma 1.9