As CalypsoCowboy mentions, VMC does not support sub-channels for OTA broadcasts. For those of us using the HTPC for OTA only (no cable, no satellite), this is a big deal, because there are as many or more subchannels as regular channels, at least in the Chicago area. Furhtermore, the subchannels have programming which I prefer over the main channels.
Note that VMC can be made to work with at least some of the subchannels if one is lucky enough to find a local cable lineup which has them all, then re-map, and do some registry "hacks" which are documented in online forums, but this is very time consuming to research and do, and it is really unbelievable that VMC does not automatically detect subchannels, and include them in the EPG.
On the flip side, I was able to receive HDTV channels without any problems in VMC, and so far (after several hours of trying), I have not been able to make SageTV work with HDTV channels (audio and video stutter and go slo-mo). I think I'm getting close to getting it figured out, but what a chore!!!!