I have just purchased a Samsung 65 in 2018 QLED tv (QA65Q6FNASXNZ) and all went well until I wanted to view HDR from my new 4K Apple TV. There appears to be an issue with the Denon receiver (X4300H) and the Samsung TV that is known about (see link below).
Does anybody have a work around for this, I have done the UHD settings on and off and played around with different HDMI ports and the best I can get out of my Apple TV is 4K SDR, as soon as you turn HDR on, the screen displays the message that the source is not supported. The same holds true for my XBox oneX, SDR is fine, but not full HDR.
Very frustrating as I spent hours trying to get it working before I found the link on the Denon website about the known issue with 2018 QLED TV’s.
I don’t really want to buy some splitters and have optical cables for audio and then plug all my devices directly to the TV - that is why I have the Denon unit in the first place and my cables are all hidden in the wall and all my devices are in a cupboard, so it is very tidy and was working perfectly until I upgraded to the 2018 QLED.
I have the same problem with the Denon X1200H & 2018 Samsung Q6NF. The moment I turn on HDR features on my source device, and HDR content begins displaying, the TV shows no signal.
Also found the same link you did on Denon's site. Samsung posted firmware on Dec 20, 2018 (1202.3) and after updating, it did not address the problem whatsoever. Denon (Marantz) says Samsung isn't playing nice with HDMI protocols. Samsung says nothing at all about it.
It's frustrating, for sure. Christmas gift that doesn't work right. Meanwhile pretty much all of Samsung's 2018 (Q & N series) lineup is incompatible with all currently supported Denon receivers when in 4kHDR/60 modes.