@Tron01 -- I've owned my 3400 since May 2020, but had both 3400 and 2170s for extended home trials on and off for around 9 months before that, first with Spendor D7 floormount speakers and then with ATC SCM19 standmount speakers supported by a M&K X10 subwoofer. My listening room is a challenge a little similar to yours in that I have a double width patio door at one end of the room and a two glass panel doors to one side of the room.
I had previously tried to get Dirac working in the room (spent nearly 3 years) and whilst I could get decent surround sound performance, I could never get stereo music to consistently sound good, with emphasis being on consistency. My yardstick for sound performance was also headphones in that I could get very consistent and pleasing performance from my Sennheiser headphones and really just wanted to replicate that performance as closely as possible from my speakers. In my frustration, I tried Audyssey (via a Denon 8500 AVR) and ARC Genesis (via an Anthem 1120 AVR), but they were no better than Dirac in all honesty.
Enter Lyngdorf and RoomPerfect with the 2170 and 3400 (the 1120 didn't exist at this time) and in my room/system, it was a revelation. Without messing around with room curves (all I seem to be doing with Dirac), almost immediately I got great results and to this day, I not only continue to be very happy with the sound quality I get, I continue to be amazed at its consistency, a goal I didn't think I could achieve. Previously I've had Arcam, Linn, Naim and Meridian components all of which had sounded good, but not great, something that most likely can be blamed on the room. AS the room is a lounge, I have no desire to put in room treatments that may or may not work. For me, RP has provided me with the solution I was looking for and since may, all I do is listen to music, no messing around with with curve design and constant REW measurements.
It is more difficult for you if you can't get a home trial, but hopefully my experience might give you some ideas at least. I've certainly not heard any of the flaws you mentioned with respect to D Class amps, instead continuing to enjoy the amp immensely. BTW, in case you were wondering, the only reason for the extended loans of the 2170 and 3400 was my indecision as to whether I would really do any streaming. I decided to err on the side of caution and surprisingly (to me), I actually stream quite a bit now with Roon/Qobuz, so glad I made that choice. Obviously that is a non-issue with the 1120 as it was always designed as streaming capable.
Hope this is of benefit to you.