This has probably been discussed elsewhere, but to me it seems utterly unsurprising that these receivers don't meet the standards of the other audio device classes reviewed here.
Consider the price, 1000 USD (or 600 USD?). That has to cover the cost of 7 high-power (for consumer) amplifiers and 8 DACs. Those devices all have to live together in the same box, sharing heat and electrical noise. They also have to coexist with circuits to handle all of the extra features that people expect: GUIs, decoders, networking devices, media playback, DSP, etcetera. These add cost and electrical complexity. Then there is the software licensing for all of the various formats the device can decode. Also, the ADC (and possibly upscaler) that converts analog video signals to something you can send to your TV over HDMI. Don't forget about the cost of all those connectors on the back, and the complex PCB you need to get them all routed correctly (how well-seperated can the traces really be with that much routing to do?). All of this needs to fit in a standard size box with poor ventilation, and if you must have a fan it had better be completely silent (and not introduce yet more electrical noise, or much more cost).
Imagine the only components were the DAC channels: that's 125 USD per channel. In the ASR reviews, 250 USD seems to be about where you start paying more for features than performance (on average). Of course, there are cheaper good-quality DACs and there are economies of scale to take advantage of. Still, it seems unreasonable to expect AVR manufacturers to achieve the same results with the same budget when you consider all of the limitations I mentioned above. We haven't even considered the amplification stage.
Imagine you had a standalone box that decoded the DTS/Dolby stream, then sent that signal to 4 standalone stereo DACs, which were connected to 4 standalone stereo speaker amplifiers. Add an HDMI switchbox (without ADC, since most people don't need one anymore). You could probably do this for 1000 USD. Not only would it be inconvenient and complex, I'd bet that the quality at that price would be comparable to the results here at best.
And to address the elephant in the room, if Amazon is selling it for 600 USD then one wonders if 1000 USD is one of those imaginary prices that doesn't really mean anything. That would make the actual cost per channel much lower. It also raises the topic that retailers take a huge chunk of the MSRP. Many boutqiue audio manufacturers primarily sell equipment through their own stores, so that huge cost to the consumer is reduced (meaning that a Schitt price is not exactly comparable to a Denon price).
TL;DR: This performance is about what I would expect considering the complexity and design restrictions of the device under test, when compared to the budget available for design and manufacturing.