I would also have to suggest Johnk's troubleshooting to determine if it is a faulty speaker that is causing the shutdown issues. I highly doubt it is the multichannel listening unless you are running the M60's and VP150 full range (large) where 4 and 5 ohm impedance dips could be causing problems with that particular receiver. This is doubtful. If you can isolate each pair of speakers for any shutdown issues also check to determine if sound is coming out of each driver and fully functional.

There have been cases in the past of a faulty woofer or other defects in the speaker that have caused receivers to shut down after a certain point.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne