GZDoom success!
Tried to use GZDoom a while back on a previous version of Trisquel but had no luck at the time. But now that I've recently installed Trisquel 11, I gave it another shot and got it working. What I discovered was that the ATI card I was using was incompatible with the OS. I tried a Geforce 1gb 610 card and it worked like a charm! I've ordered a 2gb geforce 730 off ebay for some more graphics ability. In the meantime I'm enjoying a little FreeDoom fun in an up to date source port! :D