Agreed with your concept, but would add; the X8500H will also have the same mediocre IC opamp in the filter circuitry that follows the DAC IC, and the same NJR CMOS switches to go along with the NJR volume control. The medium and upper level models have a lot of the same parts.
It appears that the use of one more 8-channel volume control IC would eliminate the need for the switches with perhaps a 6dB improvement in THD performance. A few stereo RCA inputs might have to go.
I'm pretty sure it's not even only the analog parts that contribute to the bad score.. I've said it before, so I'll say it again: look at the stopband attenuation.. -60dB? Really (the X4700 did -80dB) ? How on earth did they manage that on a 32 bit AKM DAC? None of the 32 AKM DAC's have a reconstruction filter that crappy. There must be more to it!
Actually, the only reason the analog parts of those AVR's are so complicated is because they still have analog inputs and the purists still want "pure direct" throughput to the amps. There really is no need to analog volume control chips if you keep it all digital. Would also reduce the possibility of EMI significantly since the analog paths are shorter. For all the advanced features analog is digitized anyway, so that "pure direct" mode is actually sacrificing a whole lot. In the end, you could actually end up with a much better SINAD if one would remove that crap and digitize the analog stuff as fast as possible, and keep the DA section as simple as needed for good performance.
Obviously the pure-direct zealots would hate this
In any case, I'll never buy anything from Marantz or Denon ever again. I have SR6010.. The wifi is unusable, the volume control on the device does not work anymore (which happened to me on an older Marantz amp exactly the same.. they did not improve anything in over 20 years). And one of the main channels is broken, which I only noticed after more than two years since I've always used an external amp, so it had been from the start. Feature wise it really is a nice device though.
Their standard are the published specs, and as I wrote above, even with the "bad" cap the unit fulfills them (IMO).
What specs? They really spec almost nothing..
Those AV receiver are really in a sad place imho. Where are the SMPS'es? Where are the Class D amps? At least Pioneer is trying.. not that I would buy that. It's not even that those things make it necessarily better, but it shows that the most important thing those companies want, is to put more marketing stickers on their products. 8K.. HDMI 2.1, a gazillion amps.. ever more 3D audio standards.. Just give us a decent SINAD as well.. And no, it's not about this being audible or not. If one can expect 8K video support, I can also expect top notch audio performance... meaning 100+ SINAD for the DAC, 90+ SINAD for the Amp.. Sounds only fair to me..