I don't think there's much of one...All I can see from Creative's website is the 6.1 speaker support in the Audigy2. Both have the same 24bit/196khz specs...
Far better DACs are used, it's actually a true 24/96 card this time (audigy is internally 16/48), double the 3d hardware voices of audigy/live, dvd-a playback (only way to get it on PC).
Not sure what else really as I've yet to get one.
Yeah this is correct lots of professionals apparently complained that it wasn't proper 24/96 on the audigy, so creative fixed that with the audigy2. As already mentioned the 6:1 sound is the only other new feature.