Hi TylerDCA,
I'm not familiar with H/K's latest models, but over the years all the H/K AV receivers, like the Denons, have been able to drive the 4-ohm M80s without problems of current limiting or overheating or shutting down. That includes the entry-level models. That's also true of the Sherwood Newcastle receivers, which we sell at Axiom. Like H/K, the Sherwoods have robust amplifiers that have no trouble driving the 4-ohm M80s.
The Outlaw amplifiers are also fine with the M80s so long as you don't try powering five M80s simultaneously at extremely high playback volume, as one Axiom owner did. Emotiva has had some issues with M80s, as Sir Quack pointed out. For extremely high SPLs in big rooms, I recommend Axiom's own A1400-8, which never gives up.
There is a review of a new-ish Pioneer 94 (?) at Audioholics that shows excellent performance with 4-ohm loads, but we don't have enough customer feedback at Axiom for me to unreservedly recommend the Pioneer. Previous Pioneers have had issues with 4-ohm loads, except for one model that used MOSFET output devices. That model is no longer available.
Regards,
Alan
