How to control the volume of a panasonic home theater system on my Comcast remote.?

I use comcast for t.v. and i programmed my remote to control the t.v., cable box and panasonic home theater system and whenever I change the volume for the home theater system, i have to use two remotes because the comcast remote only changes the volume on the t.v. Is their anyway to be able to change the volume of the home theater system using only the comcast remote?