You didn’t read my posts, did you?
1. You have performed measurements only at 4.12V RMS output level, which is an overkill for a processor with officially max rated output at 2.4V RMS (in the specification). It us unclear why you have decided to use specifically overloading level for the tests, there is no reasonable cause.
Reviewer from HomeTheatreHiFi, who gave Marantz 8802 “Best of Award for the year 2015” (Marantz 8805 just has some additional features, the design is pretty much similar), performed the measurements properly, just before the max output level at 2.05V, and the level of distortions was WAY lower comparing to your measurements. In addition, they have performed measurements at 5V, which are comparable with yours. But it is not a standard mode for the processor.
2. You made some wrong conclusions regarding quality of the processor and based on the overloading level, for example:
Sad because this would be poor rating even for a $99 desktop DAC let alone a $5,000 processor.
THD+N is dominated by the third harmonic which means that it will peak above the noise floor of 16 bit CD content (96 dB dynamic range). So we lack transparency there let alone for high-resolution content.
but has too much distortion as the signal gets louder:
Considering that I kept the output level at 4 volts, i.e. well below max, the rising distortion is worrisome.
Correction: “way ABOVE max”
Next test, THD+N versus frequency was a shocker: What the heck? The moment we go past 5 kHz, the distortion+noise shoots sky high. It is off the chart literally post 10 kHz. What is going on here?
There is no “heck”, it seems the processor clips earlier at frequencies above 5kHz, but again the level is completely wrong.
Thinking this may be an aliasing issue, I ran my white noise test where we look at how much filtering we get at 22.05 kHz. Theory demands that we get infinite amount of signal reduction at that frequency. This is what we get instead:
why would anyone expect to see a cut off at 22.05 kHz (44.1 kHz sampling rate) if 192 kHz sampling rate was used? It is obvious looking at the 90 (probable 96 kHz) graph. What you see is a slow roll off at 24 kHz, because the Audyssey processing (or all processing) was performed at 48 kHz. This article explains why:
https://www.audioholics.com/room-acoustics/audyssey-room-eq-interview
I searched the manual for any DAC filter setting but did not find anything. This is flat out broken. I get wanting slow roll off but this smells like incorrectly programmed filter setting.
Correction : nothing is “broken”, nothing “smells”.
We get essentially the same performance. Then again, what we have here is limited by high harmonic distortion which is likely in the analog domain post the DAC so improvements elsewhere may not show up.
Then again, 4.13 V RMS vs 2.4V max per specification.
Fortunately there is nothing drastically wrong here, sans the DAC filtering. That aspect needs to be reported to Marantz as hopefully can be fixed with a firmware update.
Firmware update for what? To see 22.05 kHz roll off at 192kHz sampling rate or update the processing to 192 kHz?
I would say buy the Marantz AV8805 because it has the features it has not because you think it will provide reference quality audio performance. It will not.
Again, wrong conclusions based on the wrong measurement results.
Correction : see the review from HomeThetreHiFi, compare Marantz 8805 with other AV processor which supports more or less similar features (Audyssey processing requires a lot of processing power), and make new conclusions.
For information: input levels for power amplifiers:
Bryston 4b sensitivity at 1.4V for 250W at 8 ohm (it has switchable gain 23dB or 29dB).
Onkyo 5501 sensitivity 1V balanced, 2V unbalanced
Proceed AMP 5 sensitivity 2.24V for full rated output (balanced), 1.12V for full rated output (single-ended or unbalanced)
And so on ...