For basic functions like Volume keys and arrow keys, 30176 will work. Make sure you have volume punchthrough to allow you to control volume via AUX, and not through the TV. When you press the volume keys or mute, the AUX LED should blink.

The Power key should respond to EFC 153. To test this, make sure you have 30176 assigned to AUX (if your remote has a red OK/Select button) or 0176 is assigned to AUX (if a grey OK button). Press AUX.
Then Press Setup briefly. Enter 00153. When you enter the last digt (3) the remote will send the IR command. It should toggle Power.

If this works, follow the 994 Instructions to assign this EFC to a key permanently.

Some discrete functions, like HDMI input, can't be programmed with the Comcast remote, nor any universal using setup codes. Of course a learning remote will work.