Believe me, I understand about hanging on to old speakers. Back in the day I had a set of dbx monitors that I kept for 20 years. Same kind of experience with them as you're describing with your Sonys.
Well, I wasn't going to give characterizations of particular brands, but since you brought it up... No, I wouldn't recommend Onkyo; I threw them in there in the interests of completeness (they only have one processor model).
So if you're interested in characterizations from someone who's extensively listened to some of those, I'll speak just of higher-end processors, not AVRs with amps: Marantz sounds pretty much the same as Denon. NAD sounds better. I don't have enough time with Rotel to say. Yamaha and McIntosh also sound better than Denon. If you're strictly about movies, Denon is fine. For movies plus music, I would take the Yamaha or McIntosh any day.
I'm very familiar with the ASR site; I like it a lot. But it has its limitations. One is that measurements, while important necessary and helpful, don't always tell the whole story. Sometimes things that measure worse can sound better. Amplifier designers and speaker designers will tell you that. Another is that with the exception of DACs, headphone amps, and a few AVRs, the equipment he reviews can most charitably be described as mid-range, because he's mostly measuring what people send him. He doesn't really review high-end processors, and he doesn't review serious amps or speakers. About the only serious amp he has measured is the Benchmark AHB2. So although the reviews there are very valuable, that site gives a very skewed perspective on certain product types.
Another important limitation is that he measured the DAC performance of the Denon with the amps turned off, because DAC performance was much worse with the amps on. You noticed that, right? How will you be using yours?
Amp performance of the Denon you referred to is not really good, except by lower standards. It's measured and spec'd with two channels driven, as are most AVRs, because their power and performance drop as you add channels. That's not good design. You'll be driving more than two channels, won't you?
So just to consider other amplification factors for a moment... You said your speakers improved when bi-amped. That implies they need good amplification. You mentioned yourself said they required high current and high damping factor. The amps in those AVRs are low-current amps. Also, a damping factor of 400 is good but not exceptional, but will you get even that in the AVR? Damping is a complicated subject, and some say its importance as a spec is overrated. But current is definitely very important. I'm talking about current available for transient peaks, not an averaged measurement for continuous drive into a load. Those Sony speakers are copies of what B&W was doing at the time; they might even have a funny impedance curve too, even with the lesser bass response and only 1 LF transducer. So if granted they need good high-current amplification with a high damping factor, you're not going to find that in an AVR. Since you know the ASR site, compare what he says about the Denon to his measurements of the Benchmark AHB2.
If you want truly high-current amplification with a high damping factor, with great bang for the buck, look at Parasound or Benchmark. Benchmark only makes one amp, but Parasound has a full range, including 5 channel amps that are so far beyond what you'll get in AVR amps that they're not even comparable. And if you want monoblocks someday, they also make the Halo JC1/JC1+, although that might be overkill for you.
Since you want the 8K for your screen, maybe something to consider is to get better amplification now, to unshackle your speakers, and then get the new processor in a while when the HDMI situation as been resolved. It would be a shame to spend a lot of money on a processor to find out later there's no free fix because it requires the whole board to be replaced. And even if they did offer a free replacement, there's still the hassle of shipping the AVR back. They're big, heavy, and you'd have to keep the box.
But yeah, it does sound like you've convinced yourself. Good luck.