Also check the surround sound settings and setup. Had a receiver not setup properly, as in no center channel connected but was active in the setup menu.
Worked fine until a program was in surround sound, then exactly as you describe it. No voices.
Are you using the left and right from a 5.1 output on the Dish receiver with the audio output set to 5.1. This would definitely cause your issue.
I guarantee I'll tell you the truth and I guarantee I'll tell you what you need to know but I can't guarantee that I'll be telling you anything you want to hear.
I've seen individual television shows where the channels were improperly mapped, but if it's happening on everything from this device... I would take a much closer at the amp.
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