Our coach has a Sony Audio/Video Control Center (STR-DE435) w/surround sound. It has several selector buttons. To get sound from our TV I depress TV/SAT button.
We also have a button for "CD" which switches to the sound source from our CD/DVD player, have you tried depressing the CD/DVD button on your theater system and see if you get sound from your CD/DVD player?
Wish I could be of more help, let us know when you find the fix...
Good luck and safe travels...