I have that Tunner and it works great for OTA (ATSC). I don't have cable so I can't test Clear QAM for you. Can you do an ATSC scan and pickup/view any channels that way? Maybe your tunner is bad regarding the QAM feature.
EDIT: I re-read your post and see that you had QAM working with WinTV. When I first hooked up my Hauppauge Colossus using WinTV it worked great but then I couldn't get it to work in MC. During troubleshooting, I noticed an error (yellow exclamation point) in the Device Manager for the Colossus. It took me a Win7 reinstall to get it right after that. After that, I went straight to MC and never installed WinTV again. Point being, check Device Manager and uninstall WinTV (if you have not already).
