I am not quite sure how you got the audio over HDMI from TV -> Panasonic as this TV does not seem to support HDMI output/passthrough. You should be able to use the optical audio out for surround purposes or the coax out for stereo.
I am facing the same issue, I do have Sony Ex500 32 inch TV and sony DAV-DZ777 hometheatre, i WANTED TO PLAY TV SOUND IN SONY HOME THEATRE SPEAKERS, but it is silent when i change the Home theatre to TV mode. I have connected red, black colour cable from TV box (audio out) and audio in in home theatre. Seems to be the connection I made referred the sony manual. Seems to be some connection problem or cable problem.