I was originally envisioning adding some DSP functions to the server software, and I'm so newb, I forgot that the *client* makes the sounds

In any case, I've had a go at an underwater effect using processed wavs, and it works! If you're curious - check out tastyspleen.net:26666. It works with axes, shotguns and rockets. Try it - jump in the water and fire your shotgun. For some reason though grenades don't work..? I forgot how TINY the sound files are!!! So the extra sounds can be downloaded in seconds, though for those who haven't been to my server there might be quite a few other files u need to dl.
Anyway, I really think this 'method' will do nicely for now, hopefully someone can explain why the alternative sound for grenades doesn't work.
ALSO: you know the sound a rocket projectile makes, when it hits a surface? I can't find where that wav is , possibly this is not in the quake C..?
OneManClan
ps Whilst people have offered to make maps specifically for the O vs D format of the game, AGR (as currently played at the ) is currently played almost exclusively on old skool maps - 2fort5r, rock2, etc.