Hi Fredk,
I usually tell consumers to ignore "Dynamic Power Output" ratings in watts, as it's a misleading spec intended to convince buyers that a stereo or AV receiver has enormous power reserves available for driving low impedances. "Dynamic Headroom," expressed in dB, is a useful spec but few manufacturers ever quote it.
Large amounts of real dynamic headroom, sometimes as much as 6 dB, which some NAD amplifiers often possessed, was based around a "loose" power supply that would switch in extra output devices or voltage rails for large momentary increases in power output. The continuous power output rating would typically be much less, often as little as 30 watts or 50 watts per channel.
A used stereo receiver or stereo integrated amplifier would likely be fine for driving the M80s, as older units often had enough heat sinking and output device cooling to handle 4-ohm loads without the problems associated with many current AV receivers driving lower impedances.
Regards,
