How do you know I wouldn't be able to hear a difference; maybe/maybe not? But, I would know
there is a difference, which for me can sometimes be enough cause me to always wonder, and thus always not feel quite completely satisfied.
Besides, I'm concerned about about the pre-amp output levels. My current rig, besides not supporting 4K video, is weak on its pre-amp outs. The AKM DACs in the AVR-X3600H and pre May 2021 AVR-X3700H have been tested out be great performers in this aspect as well. The TI chips that were switched to I don't know. I do know that my current rig, a Yamaha RX-A810, uses TI DACs and doesn't do so great.
The problem with the HDMI 2.1 bug, as I understand it, only applies to some VRR signals. Specifically XBOX-X and NVidia G-Syync. Sony PS5 VRR is reported not to be hindered. I'm not currently running any game console or PC into my AVR. Also, I should be able to get a box from Sound United which fixes the issue should it arise.
Yes, the 2.1 bug is fixed in your 3700. Also, you have an 8K capability on your output and 1 8K capable input. The 3600 is limited to 4K period. But I don't care as I have no 8K capability on anything, and don't plan to be playing in the 8K playground for quite some time. Hell, I JUST got 4K!