Do you run the M80's full band? Not that it matters now because you have a proper amp to drive them, but with the right source material, peak LFE content is what will usually cause immediate protection shutdown with an inadequate amplifier for the job. Just curious, did you try that scene with the higher ohm setting?

Shutdown, if caused by overheating would be during sustained use over a period of time and would not happen at a repeated single point.
I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne