When you lose sound, have you ever turned up the volume all the way to see if you can hear a Hissing sound coming from the TV speakers? That hissing sound is created by the output amps, and that verifies the amps work, the speakers are ok, and you're simply missing signal from the audio processor or the input you are connected to on the back of your TV set isn't sending the signal to the processor.
Turn it back down, and check the TV with more than one source. If you use TV channels, or a DVD player or a Cable or satellite box, I would be checking all of them when the sound quits. If you get sound on one, switch it back to the unit that wasn't giving you sound in the first place. If you find it's restored, then the Input switches are causing you to lose sound. Audio processors, when they fail won't let any input deliver sound to the Audio amp.
That's why we check for hissing at full volume first, then switch inputs to other equipment connected and see if that restores sound or not.
Give those tests a try. Let's see what the TV tells us is the problem.