Audio problem and proper settings for Panasonic OLED/Marantz AV-Preamp

[dvdr]

Hi
Just got my Real Vision 4k, which is attached to a Marantz AV7705 AV-preamp, going into a Panasonic OLED TX-65FZ950.
The only info on HDR support I could find for the Panasonic OLED: HDR10, HDR10+, HLG
When attaching my Apple TV 4k and watching HDR content from Netflix, Apple etc., the display says "HDR (PQ)" and I can set ATV4k to 4:2:2 and 4k/60.

With this information, could you be so kind and give me a clue, what the best video settings for my Dune HD Real Vision 4k are, considering I don't know, what the AV-preamp's capabilities are (I have set it to not convert any video = "pass-through" and not activating any additional processing by its video processor).
I also am uncertain about the right settings for the Dolby Vision options, since my TV obviously does not support DV.

Also, if we're at it, could you maybe give me a hint on how to correct the following audio problem:

I use the OLED only as a display, sound is processed exclusively done by the Marantz AV-preamp. Still, when I switch on the Dune, sound comes from the TV's intergrated loudspeakers. I have to go into the TV's settings, select audio output options and change them from "TV" (=integrated speakers of the TV set) to "Home Cinema" (=all sound by the AV-Preamp, this includes ARC). Only then, sound is processed and delivered by my AV-Preamp - but not always: often, after changing back to the proper "Home Cinema" setting, there is no sound at all even though the input monitor says, that it receives a PCM signal. I have to reboot the Dune and switch the TV and the AV-Preamp off and back on to get sound to my speakers.

I never had that issue with my Apple TV 4k or Satellite Receiver - once set to "Home Cinema", the setting never changed by itself. Why does the Real Vision 4K obviously force/activate the "TV" audio setting? Does it mess with the Audio Return Channel options and how do I prevent that?

As for Audio, I have a suggestion, as well: what do you think of introducing an audio-option to deactivate the volume slider? Reason: in many cases, it is not needed - like in any home theatre setup, where users control volume on their TVs or the AV-amps. Having  volume slider in the Dune's software, only introduces all sorts of processing, that can affect audio quality. So why not shut it off and have "unity gain" from the Dune?

Thanks for helping me in the matter!

[futeko.com]

ARC can be disabled at Setup - System - Others. When disabled it shouldn't interfere with the TV.

With a non Dolby Vision TV the best setting for Dolby Vision content will be VS10. This will output whatever HDR content you throw at it, including DV, as HDR10. Setup - Video - HDR and Dolby Vision Settings - Dolby VS10 engine always.

[dvdr]

With a non Dolby Vision TV the best setting for Dolby Vision content will be VS10.

Thank you for your advice - now I noticed a further problem in my setup: HDR content has faded, greyish blacks, "dark" movies look really bright. This applies to the "Auto" setting as well as your recommended "VS10" setting. As a reference, I used normal BluRays and a UHD BluRay disc player with the normal and UHD BluRays as well.

Thanks to your ARC advice, I discovered a big section of picture options on Setup - System - Others.

There is an option to set HDMI dynamic range from "Auto" (which was set as default) to "limited" and "full". If I remember correctly, this (maybe in former days?) had to be set to limited (16-235), otherwise blacks would be crushed. But here, when I manually set it to limited (something, that my AVR or TV also seemed to "request" at the "Auto" setting), I had the same effect of a very bright picture with greyish blacks (even the black levels of the cinemascope masking seemed raised). When I manually set to to full (0-255???), the picture got way darker and the greyishness disappeared. This resembled, what I saw coming from my UHD BluRay disc player.

Could you be so kind, and please shed some light on this?
Thanks!