The versa-jack is one handy feature. I really like it, allows me to switch from 4 speaker surround mode to headphone only with a couple clicks of the mouse .
I've had the following sound cards in this system with this same set of speakers (Altec Lansing ACS54's)
SB AWE 64 (ISA card). Decent sound quality. Nothing to write home about
Xitel Storm Platinum. Good sound quality. Games sounded better as well.
Santa Cruz. Supurb sound quality. I can definatly tell a difference when I listen to "Lateralus" or DSOTM. Games are amazing, especially Half Life (for some reason). There can be the sound of dripping water in front of you, and as you walk past it, it moves behind you. DVD movies sound supurb as well.