the HDHomeRun will only work with channels that are unencrypted on the wire.
By law, this means:
* ABC
* NBC
* CBS
* FOX
* PBS
* local community cable access channels
* CW
pretty much everything else is encrypted. Sorry bro.
The bigger issue dealing with cable is that often the cable companies mangle the PSIP stream (the part of the stream that gives program identification and channel identification), so what you see as a channel number on a cable box will most likely not be the same as what the actual QAM channel number is (i.e. my cable box says that FOX is 4, when I get it over the air, it's 25.1 ATSC, and on my cable box currently, it's 74.1 .. it has moved twice.) ... THIS IS ESPECIALLY IMPORTANT WHEN SETTING UP SCHEDULES DIRECT LISTINGS, they will not match up, and you have to spend some time in MythWeb, matching channel IDs to your channels so that the guide data will go into the right place
This is why I got a large hi-gain antenna for OTA HD stuff.
-Thom