At R00tli2k's link you can create a comparison table (scroll all the way down), the AVR-X6400H can still be selected and thus compared with the AVC-X6500H.

Differences: power amp setup, web control, Amazon Alexa, setup wizard, speaker terminals gold plated, no FM/MW tuner. The connections are slightly different. Both have network audio streaming, AirPlay 2 and eARC compatibility. It is unclear to me whether an extension was added to the HDMI standard (which one?). HDR10 instead of HDR is just more specific, I understand.

The download "Product Information" states "11 monolithic amplifiers" for both models, and both amplifiers are described as having "11 discrete power amplifiers". A slightly better description of the different power amplifier separation at Denon can be found in this forum post with a quote from Denon:

http://www.hifi-forum.de/viewthread...

According to the comparison table from Denon-HiFi.ch, 06.12.2018
AVC-X8500H: Monoblock power amplifier construction yes, L/R separated
AVC-X6500H: Monoblock power amplifier design yes
AVC-X6400H: Monoblock power amplifier design no

Compared to its predecessor, the X6400W, the X6500W has a monoblock power amplifier design! + other small improvements!

Here in the link you have an overview... what else is better ^^

https://www.denon-hifi.ch/chg...