Erzinicnik has already written a great answer:
...to which I can only add one thing. You,
, have a superb AVR which can pass through* the 4K HDR Signal, so you don't need to worry about it. All you need to do is configure BOTH the TV (turn on "HDMI UHD Color" in Expert picture settings) AND the AVR ("4K Signal Format" to "Enhanced" [http://manuals.denon.com/AVRS730H/NA...Ysvvlcemq.php]
NB: This is not the default, just like with the TV it's not the default. Older 4K-capable Denons like my 4200W are different, there's no switch, and they are effectively locked to 'Enhanced' mode).
[EDIT: that is a mistake, you have nothing to configure on the AVR
X4200H - 2015 model (no dedicated <4k Signal Format> setting)
X4300H - 2016 model (no dedicated <4k Signal Format> setting)
X4400H - 2017 model (dedicated <4k Signal Format< setting)
* We are all abusing the term "pass through" here. If an AVR doesn't explicitly say "Supports 24p/3D/4k/HDR10/HLG/White Rabbits pass through" then it won't pass [the 3D/4k/HDR10/HLG/White Rabbits information].
An HDMI port is either decoding or transmitting (it can't do both), so as long as picture and sound are encoded on one cable, the AVR has to decode the stream, separate the audio, and then repackage the picture info back up for transmitting to the TV.
If any pic info can't be decoded, then that info is discarded. This is why Denon need to issue firmware updates to add support for HLG "pass-through" and dolby vision "pass through". Each and every time something new is present in the signal, it needs to be explicitly added to the "decode-repackage-transmit" routines.
"Pass through" is a misnomer, because there is no bypass: only "decode-repackage-transmit" - whether the AVR adds an on-screen menu, or not.
So UHD-Blu-Ray player manufacturers are proving two HDMI outputs as a courtesy to some users, who have a very expensive AVR which can't decode-repackage-transmit a signal containing HDR. This avoid them having to throw away or replace a perfectly good AVR which, as it can pass 4K otherwise, is probably very new anyway. Ie, lots of people are in this situation. Hence the 2-HDMI output workaround