If your Comcast remote has a red OK/Select button try assigning (video) 21245 to AUX. This code works with AMW DVD players.
Check buttons other than volume or mute, because the Comcast remote will send those to the TV by default, which is called Volume Punch Through. If you want the remote to control AMW volume/mute, read the Comcast VPT instructions, or use the 993 command instructions here:
www.hifi-remote.com/forums/viewtopic.php