Well, sound is off in fact. Its weird because on OS 0.3 I did not have this problem.
I am using the same source as before: ZDOOM on GS for Brutal Doom and other mods!
I will try to find out what is the issue but its still all very cryptic to me.
Did something changed with the sound drivers in OS 0.4 and 0.5 ?
Does the GS support FMOD ?
Also, I was able to get SOME sound working (only the music), by setting the sound playback to Timidity++.
I do not understand why this is so complicated! It was ok on OS 0.3 but since OS 0.4 its not. The dev could help me with this!!!