I have an 11 month old, Samsung 82” QLED Q70R. I recently purchased the new Sonos Arc and I can not get Dolby Atmos to work. 
 

TV Setup - I have the Arc connected to the TV via the HDMI 4 (ARC) using the HDMI cable Sonos provided with the speaker. (It’s not and eARC port, but according to Samsungs website it supports Dolby Digital+ and Atmos. In the TV’s “expert” sound settings, I have the Dolby Atomos Compatibility box checked, and when I connected the Sonos Arc it said “Atmos enabled device detected.” Yet when I go to the Digital Output Audio For… setting, it only allows me to select Dolby Digital. 
 

I am currently using an Xbox 1s and Apple TV 4K for streaming, Netflix, HBOMAX, HULU, Disney+, etc. When I go to the XBOX settings, I have HDMI Audio set to Bitsream Out. However, when I go to the Bitstream format setting, whenever I select Dolby Atmos for home theater or DTS:X for home theater, I get a message that says: “Your receiver doesn’t support Dolby Atmos for home theater”

Sonos products used- I have a Sonos Arc, Sonos Sub (gen1), and 2- Play3’s used as my rear surrounds. I have never had any issues getting my Sonos products to work. What Am I Missing???