I've seen some people in DIYAUDIO forum replacing opamps and caps on their soundblaster Audigy. They were mostly the KX Project crowd. The main chip, they can't replace it... but there are things that you can replace. (I didn't say upgrade.... no one really knows if it really "upgrades" the sound quality)
Years ago, I've modified my ATI Videocard's RGB output stage.. (got rid of DC coupling caps) That wasn't very fun. It's hard to find such a small tipped soldering iron and my hands are not all that steady.
I know that Auzentech X-Meridan has user replacable Opamps and Caps.. but
Better to have SPDIF output to a decent Preprocessor, IMO.