Non of the Comcast remotes or set top boxes are RF capable. You would need a 3rd party solution. Most users go with a wireless or wired IR repeater solution available from many suppliers and brands.
The latest DCX3400 and RNG110's have a IR receiver port on the back for short (10 foot or so) extendable IR receiver if you are hiding the DVR. They work with the IR receivers that come with the DTA's. IR receivers are also available from 3rd parties.
I use a Xantech wired IR system in my home.
