*****(curse-word), had it on 4k HDR for a while this afternoon. Even both UHD and HDR vignettes.
But unfortunately it didn't last.
Don't know why it is not working anymore.
I'm gonna look for another receiver, this one stinks, linked with the Samsung 55Q9F.
(Quite possibly a HDMI-CEC handshake issue; I asked Denon_UK about it, also Samsung).
Did you ever get anywehere with this? I have still been chasing this between Denon and Samsung. I was promised an engineer call so he could look into it and still nothing. 4 weeks ago after spending 4 hours on the phone over 3 calls to the technical experts on a live video chat showing the issues.
I've found a temp fix but only applicable if you can do with not requiring ARC.