Ok, stick with WinTVCap for now. I'll setup my system so I can properly test using the PVR350 tuner. We should be able to get this problem sorted over the next day or so. I use svideo on my PVR350 and can only receive one channel via the tuner, but I should be able to sort out something to help me test it.
With this initial work around to get the PVR350 working with LiveTV it is very slow starting (and changing channels), and can take about 10 seconds to get started. I'm working on improving this. I've emailed you a tool that should give me a little information on whats going on with live tv.