[RickM]

I'd also say it's the receiver. Most likely heat related. The louder you crank it the hotter the output ICs get. Either it's supposed to shutdown at the level you have it at or it's happening prematurely.

If you open the unit (probably not worth the effort nowadays) you'd spray component cooler on the suspect IC upon failure....it would most likely come to life until it heats up again. After you identify the culprit you replace.

However, it sounds like you may be asking for more than your equipment can handle. An aux amp may be your best route.