I realize this isn't a supported application but I was able to passthrough a brand new Hauppauge 2250 TV tuner card and Windows 7 Media Center (32 bit) recognized it long enough to detect/confirm the TV signal but when it went to record a show later MC said it couldn't because there was no tuner available. I tried setting up TV again in MC but it can no longer detect a tuner at all. FWIW, the device is there and functioning in Device Manager, and I'm able to re-install the drivers no problem but that doesn't fix the problem.
I'm wondering if there might be some resource sharing that happens to make this passed through PCI device "disappear" for an app using it in some situations. Is there anything I can try to change with respect to preventing resource re-allocation related to PCI passthrough? For what it's worth, I've tried reserving the memory for the VM. It didn't fix the problem but maybe I have to re-install with it on for it to work. Before throwing that Hail Mary pass I wondered if anyone had other ideas of things to try.