Impressively thorough review.
Like others, I'll have to come back when I have adequate time to fully absorb it!
Scanning through it, there were two things that came to mind.
1) The following quote is from the power analysis section:
You can see the protection circuit kick on during our ACD tests, purposely limiting power to 65wpc. In short time, there is no doubt in my mind forum lurkers seeing this will pop up on our site or AVS Forum bashing Yamaha, not realizing the design purpose of power limiting a multi channel amplifier in a compact chassis, or the reality that real world program material will never trip this limiter circuitry.
Is there someplace where this has been discussed in more detail? More specifically, to use the comparison with the UPA-7, it stands out that the UPA-7 does not have such protection circuitry. Should it? You mention "compact chassis", and I suppose with the added electronics of the processing, the Yamaha is effectively a good bit more compact than the UPA. Is it a simple matter of preempting a situation which would lead to overheating, or more complicated than that?
2) I was hoping to see a "gutz" photo, or read a bit about the amplifier design/components to see how they managed to get so much power into such a small form factor at such a low weight (the UPA-7 at 66 lb and Yamaha at 37.5 lb). Do you know what class of amplification is used?
With the comprehensive treatment you gave for this review, I feel a bit reluctant to ask for more information, but how does Yamaha get so much power out of so little weight and size? Are they using some variant of Class D amplification? Is this common in new receivers?
Thanks,
Kurt