Which Comcast system & remote from them are you using exactly?
Bob is correct however- get a Harmony if you want the real deal.
I recently bought 2 new LED TV's, an Element and an LG. Both of these TV's require the use of 2 remotes! One to change the Channels, and One to adjust the Audio. I have Comcast Xfinity Cable and my last TV did everything from just one Remote! I'm wondering if there are any Brands of TV's, that will work with only the one cable Remote?