Yes I believe its an onboard sound setup as I have no other sound cards or etc. I tried adjusting the sound setting like you said jimbuna but they only go from
-40db to 0db on mine. (well I uninstalled and reinstalled without the GWX yet.) I am thinking about maybe copying some of the sound files from the unmodded version before I install the GWX and maybe copying some original sound files into the xpansion. Not really sure how that will work lol. But yea basically all sound works fine except the engine sounds and some ambient sounds inside and outside the sub(sea crashing, waves, etc.)
Voices work great, torpedo firing, ship explosions, etc. all work pretty good. I turned the FX volume up pretty loud and my speakers and I think I could hear a faint engine noise, but it doesn't seem very loud at all. Were real u-boats really this silent? I figured they would sound like the do before the GWX is installed and all clattery and loud. Thanks for the info and I will keep you updated.