This is really interesting! I have one M1 that is around SN 1450 and runs pretty hot - but can keep my hand on it when running. I have another that is around SN 1250 and runs much hotter and I can barely keep my hand on it. They are both running in bridged mono config. You have me wondering if the lower SN amp is actually running in bridged mono, though? I must say that the system sounds pretty stinking good though! I guess I should pop the tops on these and see if I recognize any of the internals you described.