Hi GraemeL,
All of us here at Axiom prefer to err on the side of caution in advising customers which brands of AV receivers will consistently work well with the 4-ohm M80s. The problem that has shown up consistently from customer experience with brands like Yamaha, Onkyo, and some Pioneers is that these brands will tend to prematurely shut down or go into severe current limiting when driving the 4-ohm M80s. The Denons, Sherwood Newcastles, Harman/Kardons, NADs, Rotels and a few others do not do this.
We can't possibly test all AV receivers with the 4-ohm M80s, but we have accumulated enough evidence from customers and in-house testing to suggest that certain brands may be problematic with low-impedance loads. So rather than risk disappointed customers, we simply recommend the brands we know work flawlessly driving the M80s to very loud levels without current limiting or shut-down.
As to Sound&Vision tests, you have to read the very fine print on the tests into 4-ohm loads. Some Onkyos have shown a consistent pattern of going into current limiting with 4-ohm loads, which reduces the power output dramatically. And you cannot rely on a test with one channel driven at a single frequency (1 kHz), the "standard" often quoted in some manufacturer's specifications.
Yes, your Yamaha may drive the 4-ohm M80s at reduced power output. But I'd rather you get a brand of AV receiver that we know will not give you any problems. That is what I advise Brent and the other audio experts at Axiom to tell customers.
Regards,
Alan
