Receiver shutting down during high loads

Thanks Flrnlamb and Elevick, I have not changed speakers for at least 7 years (KEF Coda 7's as mains and simple JVC surrounds without a sub). I did choose "small" on center speaker, I have the level at MAX, but I've had it there for the past number of years with no problems (until now). I am adding a subwoofer, so I don't ruin my Coda 7's, but since I haven't had one, and haven't had any problems until now, I don't think that's it...
I have run the speaker check mode, and everything seems to work, no negative polarity issues, but I must admit I don't know what a "dead short" is or how to check for that...
It certainly seems as though it goes into a shutdown/protection mode. Again, this is a brand new problem--it's worked flawlessly for 7 years or so...

As an update, I watched the scene again (scene 7, The Interpreter) and everything sounded fine for about 3 minutes when the audio seemed to drop out by maybe 50%...30 seconds or so later the receiver shut down... I believe it may need new capacitors as I cannot find any shorts in my speaker wires. Also Elevick, it is a 110v unit with no external transformer.

Another update, the repair shop said this looks like a digital problem. Does this sound right? The unit overloads in Prologic as well...