In DXDiag, you need to set the Hardw.Acc-slider back 1 notch, exit DXDiag, and test SH3 ...not the audio-tests from DXDiag (allthough that never hurts)!
If the problem with SH3-sound persists, load DXDiag again, and put the slider back one more notch (which should now read "basic acceleration"), and test SH3 again.
On my old audio-setup (Philips SeismicEdge soundcard), this cured my audio-problems with SH3.
My current setup (nForce2-Ultra sound) runs without issues on full H/W-acceleration.
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