Alright, guys, I think me and c0d3h4x0r have finally gotten to the bottom of this. It turned out to be driver issue. The newest Creative drivers for my soundcard and the newest SoundMAX drivers for my onboard chip both exhibited this issue. As soon as I uninstalled either one I had installed for testing and used the standard Windows HDAD drivers, this issue disappeared completely on two of my desktop machines here.
Yes, it appears only Realtek and Microsoft have gotten it right so far--Of course, I'd also like to hear that from CMedia, IDT, and Sigmatel chip users. Funny thing is, I immediately also noticed more FPS (beyond the usual margin of error) in both recent games and demanding emulators such as Dolphin and PCSX2. So the solution for now is to use Windows' standard HDAD drivers and go bug SoundMAX and especially Creative to fix their buggy mess. It's sad to not be able to use your manufacturer's drivers, but hey, if there are alternatives available...

By the way, FireBrandX managed to fix his problems via upping the 2D clocks of his ATI 5770 HD card's CCC profile. He was actually suffering from a known problem which can also cause stuttering issues watching 1080p movies via DXVA.

Last edited by gummybear; 04/19/10 06:32 PM.