Finally, HDTV is completely working in my MythTV setup.
The pcHDTV 3000 card is working nicely with the DVB drivers.
My problem was playback performance. After switching to nVidia cards, this is fixed.
I got a nVidia Geforce 6800 card for my main workstation. Overkill for MythTV, yes, but it is a stellar performer with games. Absolutely great. I can run my games at 1600×1200 to take advantage of the native resolution of my flat panel, and they all work great — no framerate problems at all.