MC can receive HD channels just fine. I receive FTA 1920x1080i H.264, 6 channel AC-3 channels with no problem here in Australia.
However, as CountryBumkin said to you previously;
You can not view encrypted channels with Media Center program - perhaps that is why some channels don't play.
If your HD channels are encrypted, MC can't play them. This is, of course, a DRM and licencing issue. It won't be solved any time soon.
If you believe that the HD channels aren't encrypted (Copy Once), provide some more information about your location, your service provider, which channels are not working, and anything else you think is relevant. We already know you are using a HDHomerun Prime.
