Hi DavidH,
In the past, lower-end Denons, Sherwood Newcastle, NAD and Harman/Kardon AV receivers have all driven the 4-ohm M80 towers without overheating or shut-down problems, so long as they are not operated beyond their output limits (i.e. trying to fill unusually large rooms with absurdly loud playback volume). By "unsually large", I mean rooms larger than 2,500 cu. ft--length x width x height.
Other brands that have experienced no problems with M80s include Rotel and Outlaw Audio.
Lower-end models from Pioneer, Onkyo, Sony and Yamaha have in the past not been stable driving 4-ohm M80s.
Regards,
