I asked this question over at AVSForum (because nobody had replied to me here).
This is jdsmoothie's response: "If you change the AMP ASSIGN setting after running Audyssey, then Audyssey is usually disabled until Audyssey is run again under the new AMP ASSIGN configuration. More than likely...
I bought the x3700h and I'm using it in preamp only mode with a 5 channel Anthem MCA 50 amplifier.
The Audyssey room correction works well, and the system sounds excellent (5.1).
i have my unit connected to the internet (and have done some firmware upgrades that way since I've had it).
would that have required registering my unit, or is there some further step i should be taking?
i believe i needed the serial number of the unit to connect to the internet.
I keep stuff forever, so I wanted to future proof (as much as possible).
When I was looking to buy, the AVM 60 was over four years old, and the successor unit (AVM 70) was nowhere in sight.
I was also wondering what the AVM 70 MSRP might be, given the price of the AVM 60.
It came down to not...
Maybe hold off on the Denon until they resolve the HDMI 2.1 bug.
I personally bought the x3700h and I am using it as a preamp with an Anthem 5 channel amp (MCA 50).
I don't know what the 6700 offers in preamp-only mode that you would need over the 3700, you might be able to save some money...
I can't see me having 4K 120 or 8K 60 sources any time in the near future (or distant future), but I'm looking forward to getting this resolved regardless.