basically to have 'very high quality sound' every component in the sound system must be as of high a quality as possible. so if you're buying an audigy 2 ZS (or whatever the latest is called), buy the top of the range speaker set, use digital input etc...
but for us, listening to mp3s (which only consists of two channels), a plain AC97 will do. i've used AC97 and SBLive on my comp and i can't discern much of a difference using an altec lansing 45.1 2.1 speaker...
IMO, as long as we dun invest on $10,000 super-tweeters and audiophile-grade amps, it doesn't really matter if you use AC97 or SBLive or Audigy. as long as the sound is clear for mp3 listening at a normal volume (which it is on all those chipsets), then it is fine.