So it turns out that the board supports up to six channel audio, and I just never noticed the additional audio jacks before complaining about the sound problems. An idiot is me. Still, it's not all my fault. While the onboard audio does up to 5.1, the lack of Vista drivers (and my inability to force the XP drivers to install) limit me to stereo, despite me being allowed to configure for quadraphonic (as befits my speaker system). Odd.

Of course, I have to determine this after buying a separate sound card. Then again, it was a cheapo $20 card anyway, with questionable Vista support itself. At least I can return it for store credit.