I don't know anything about M80s.
but I enjoy Onkyo 900 with Westlake BBSM8 which has nominal 3.8ohm with min 2ohm. I just set Onkyo to 4ohm, no any problem even I turn vol gain to +10dB!
before Westlake, I used Tannoy which is 8ohm.
my sp 
doubt smallest Denon, say 1508, can drive M80s at 4ohm?
Quote:
JC is absolutely correct about not using the Onkyo 805 (or any Onkyo AV receiver) to drive the 4-ohm M80s and I regret that Brent suggested you could do so. As JC has advised you, the 805 will be fine driving the other channels (a 6-ohm load presents no problems for any AV receiver; it's as benign as an 8-ohm load) but you will need a separate 2-channel power amp for the M80s if you continue to use the Onkyo.
In Brent's defense, it's extremely misleading for Onkyo and some other manufacturers to suggest that their receivers will drive 4-ohm loads, THX "certified" or not. Moreover, the manufacturers (almost all of them) use the totally bogus "dynamic power output" spec to mislead consumers into thinking that an AV receiver will not only drive 4 ohms but even produce hundreds of watts into as low as 2-ohm impedances. The receivers will do so for a tiny fraction of a second, then shut down!
The only "dynamic" power output spec that has any meaning is "dynamic headroom" into 4 ohms, which is expressed in dB. That spec is seldom stated because the receiver's amplifier is rigorously stressed in that test.
Ever since I joined Axiom five years ago, I've been warning against using Onkyo AV models for the 4-ohm M80s (based on Axiom customer experience and lab tests by some magazines) as the Onkyos either go into severe current limiting when set to 4 ohms (producing perhaps 30 watts per channel or less), or they shut down.
As I've explained in previous posts, the AV receiver brands that Axiom has found able to drive the 4-ohm M80s without severe current limiting or shut-down are: Sherwood Newcastle (which we have bench-tested and which Axiom sells on-line); Denon, Harman/Kardon, B&K, Rotel, NAD, and McIntosh.
The AV receiver brands to avoid if you want to get the 4-ohm M80s are: Sony, Kenwood, Onkyo, JVC, and Yamaha (except for one or two models).
