I'm sorry but I'm somewhat confused.
I can get it to recognize the DTA and I can Control the TV from my computer, so channels change up and down and volume works.
But I cannot get the channel to change on the computer.
Sounds a little contradicting.
I have a comcast DC50XU DTA on every tv now in my house so that they can be hooked up the the cable.
I checked the Setup Assistant, it doesn't appear that "Comcast DC50XU DTA" is listed as a valid option. Which options did you chose that got you the limited functionality?