I have an Asus P5B Deluxe and I'm running it with pretty standard 2-channel speakers and I find the sound quality apalling. It crackles as though there's a lot of interference, but is much worse with games than with music.
It's not the biggest problem in the world as I have an old sound blaster card I can put back in, but if anyone knows of a simple fix I would appreciate it. Or has no-one had the same experience?