remote code for comcast box

I just got a Sony STR-DN1040 receiver. I would like to use the Sony remote that came with it (RM-AAP102) to control my Comcast box (Motorola DCX3051). I've tried the remote codes listed for Motorola in the Sony user manual, and some work to the extent that they will enable turning on/off the Comcast box, but the TV CH button won't change channels, and the play/pause/stop etc. buttons don't operate the DVR. Has anyone tried this ? Is there a remote code that will work the way I'd like it to or is this an exercise in futility ?

Thanks,

Oscar Hobson