Larry, the M2200s easily drive M80s to beyond safe listening levels. Have you measured the actual sound levels with an SPL meter when this occurs? 0dB on the receiver being used as a pre-pro doesn't answer the question.
There have been occasions in the past when an intermittent short in the wiring caused a shut-down, rather than overheating, so this should be carefully re-done.
Also, if in fact there was overheating at less than excessively loud and prolonged use, it would indicate that the M2200s aren't being given adequate space for ventilation.
There should be no need for additional amplification.
