Don't bother upgrading...really the only improvement on the audigy card is 24bit playback. Garanteed you have nothing encoded at 24 bit
Check a few things:
1. Quality of cables used... - use good quality (maybe monster or equiv with gold plated ends)
2. Volume level's - Is the computer volume set to high? I would suggest a 3/4 volume level and use the amps to power the rest.
3. Audio application - plugins can enhance the sound such as eq's etc.
ry