All the DTA's along with the newer full cable boxes use the same IR codes. These use the newer XMP protocol, which many universal remotes do not know about. Only the latest universal remotes know about the XMP protocol
So the bottom line is the remote must be newer like 2 years or less and still know about the XMP protocol. Anything that doesn't will not work no matter how many codes you enter into it. it can be very well not be compatible depending on the age and if it supports XMP.
If the remote is newer, it would be listed by the remote Mfr as a Comcast remote, Comcast DTA or some similar term. Once the code is found, it will be the same for all DTA's, RNG full boxes and Motorols DCX series full boxes.