Well I have a live 5.1 in my PC. I use it for audio capture only. Which I have to say its pretty damng good at.
As for musical applications, The 5.1 instrument patches are OK (8MB set), effects are fine for mucking about, but my Yamaha MU100R grinds it into the dust and spits on it for serious realtime effects / tone generation quality :-D
Back on topic, I don't think the SBLive / 5.1 have hardware MP3 decode / encode but the DSP may give a degree of hardware 'assist' depending on drivers etc.
Anyway, MP3 playback is not really much of a processor killer these days. Even my 'obsolete' 350MHz K6-2 is fine, requiring about 2-5% CPU time.
