Nforce2 audio is the same audio used on the nforce1s and it was said at the release of the nforce that it was roughly on par with the Live. But I think most slightly prefer the quality of the Live over the nforce apu.. but try both.
But if it was me, I'd use the nforce audio and forget it.. its integrated (less possible conflicts) and can do real time dolby digital (like the xbox).
The only card worth getting to use instead of the nforce audio is an audigy. Thats what I'm going to use on my nforce2 when it gets here, only because I already have one.. if i didnt i wouldnt buy one.