There are 2 problems with the SB Live 5.1! cards (yep I've got 1),
1st if you use them to decode to analogue, the A-D's are really pretty crap in HiFi terms, but I've yet to identify a better option - there are cards with enuff A-D's for 5.1 decode, but they appear lack facilities like bass re-direction etc. that you get with the SB card
2nd. Even if you use digital out to a separate decoder, it appears from many discussions on this forum that the SB Live cards all provide digital out be going D-A-D, and not just straight pass through, so you sdtill get hit by the poor A-D quality.
Its not what you do - its the way that you do it