Unless your MP3's are well encoded at 320kb/s , and you have really good (eg NOT computer) speakers, I doubt you will hear much difference between the live and the audigy. Really any decent soundcard for that matter. Audio quality is a chain. For most computer music listeners the weak links are in:
1. Encoding to lossy compression schemes
2. PC speakers designed for gaming
Gaming speakers need to be designed to handle sharp transients. They also tend to hype the bass enormously.
Most souncards are nowhere near the weak link. But if you just want to spend the money, go for it!
I am sure you will get a lot of responses from people saying how much better their card sounds for music. I am sure they beleive it. I'd have to see a blind a/b comparison of two cards using Altec Lansing speakers and 128kb/s MP3's to be convinced.