The EGS 7.1 files you got from aminet won't install properly unless you manually edit the install script. The only version I have gotten to work with my spectrum 28/24 card is from
Installers Heaven. The version is 6.2 and the files are good. You can also get another version from the remenants of the GVP site but the dms file for disk 3 is corrupt. I managed to get a good file from the
Internet Archive but this version of the EGS software didn't work on my A2500 and the other one did.
I managed to get both the EGS and CybergraphX software going at once but it was really unstable and the EGS workbench wouldn't work at all but the rest of the EGS software did if I started it from a native Amiga workbench but if I started it from a CybergraphX workbench the card would output garbage until I turned the machine off and on again. I now have both systems on different partitions. CyberGraphX or Picasso 96 is the way to go if you want a decent workbench. The EGS workbench only works well in 16 colors. Anything beyond that is way too slow. The paint program isn't too bad once you get beyond the primitive interface. I use a lot of older software in my A2500 and compatibility is important to me but if you're running OS 3.9, I would use CyberGraphX or Picasso 96 and keep EGS on a separate partition for the occasional moment you might want to use it.