Why you guys are getting all worked up over decibel levels is baffling to me. That is irrelevant to what’s happening. The amps or part of the assembly is defective. Send them back or get your money back. If the amp is rated for a continuous 4 ohm load, and it shuts down driving a 4 ohm load, something is wrong with the speaker (short to ground), something is wrong with the amp, or the manufacture fudged their numbers. They should not be going into over current protection driving M80’s. Drivers are not some sort of mystical electron vacuum that sucks more current out of an amp that it is designed and rated to supply. They only draw available max current supply of the connected amplifier’s transformer, which your amps are not supplying without shutting down.

The simply fact that your Denon did not shut down should tell you something.