ATI Theater 650 Pro Combo audio issues

[pioniere]

I have an ATI Theater 650 Pro Combo installed on a Dell Dimension 9200, running Vista. The video works fine, but the sound quality is horrendous. The best description I can come up with is that there is static occurring at certain sound frequencies and not at others. The Dell has Sigma Tel audio installed, which works fine for everything else, including Vista's Windows Media Center.

I realize that the 650 is not on the supported list, although I have read plenty of posts from people who are running it without issue.

I wonder if anyone has any suggestions as to how I might resolve this? I am actually planning to downgrade to XP (Vista is a performance pig), and wanted to get SageTV instead of buying XP Media Center. But if I can't get this fixed, I may not have a choice

Thanks!