I’ve a Samsung Q80R as well. I can get nothing but 5.1 out of the Arc and it says on the Sonos app system setting that the Arc input is stereo 2.0 from the UHD Blu Ray. I tried resetting the TV to factory settings and briefly it showed that I could access Dolby Digital plus in the settings rather than PCM. But as soon as I set up Netflix again I noticed no Atmos note on movies I knew had it, went back to settings and it had reset to PCM with the Dolby options greyed out again.

I bought the Arc knowing I didn’t have E-ARC HDMI on the telly but had read that Dolby Atmos was available through just HDMI ARC so I thought `you beaut! I’ll have that then’. 
But telly says nooooo.

@jam9 id be curious if the splitter works. Everything I’ve read would suggest not but… worth a shot a suppose! I’m curious. 

Mine arrived two days ago and I have a qe49q70r (2019).  It doesn’t appear that I'm get ATMOS through the built in Netflix app (I can’t see the ATMOS logo in the Sonos now playing screen.)

Where do you look to see if you’re getting DD or DD+?

thanks.

Just to follow up on this post, I’ve pre-ordered one of these: https://www.hdfury.com/product/4k-arcana-18gbps/. It’s currently in development but is supposed to allow you to split output from an HMDI source to your TV and to the Sonos Arc via eARC. I don’t like having to spend so much when I think Sonos simply could have done a better implementation of connectivity to the sound bar, but if this works, I’ll be happy. In the meantime, I am enjoying getting Dolby DD and the sound is generally very good.

I think you’ve gotten some good answers here and I’ll echo @jam9’s recommendation of the HD Fury Arcana (https://www.hdfury.com/product/4k-arcana-18gbps/) for the following reasons (based off your original post and some of your other comments): 

• While some people have gotten lucky getting Atmos from Apple TV over regular HDMI-ARC, because of the way that Apple sends Atmos (basically LPCM in a Dolby MAT container - don’t ask) whether it will work for you or not is highly dependent on your TV model’s audio capabilities. Arcana takes your TV and its audio capabilities / limits out of the mix and sends whatever the Apple TV is capable of directly to the Sonos Arc. 
   
• There’s a lot of discussion about “full” vs. “limited” Atmos, but Atmos is Atmos regardless of how it’s being transmitted. Yes Atmos can be sent over “lossy” Dolby Digital Plus or over “lossless” Dolby TrueHD, but, as another poster very correctly said, it’s highly doubtful you’d hear a meaningful difference on the Sonos Arc. 
   
• And, since you don’t use Blu-ray Discs and only watch via streaming apps, then you’d only ever be getting Atmos over lossy Dolby Digital Plus anyway, so it’s a moot point. 
   

So, in a nutshell, the HD Fury Arcana is, so far, the only sure bet that will give you the full sonic capabilities of your Apple TV when paired with the Sonos Arc (short of buying a new TV, and even then we’re still seeing plenty of issues with eARC-compatible TVs). I’ve got an Arcana on pre-order myself for my Apple TV 4K / Arc / Vizio E70-F3 setup and I’m looking forward to receiving it. 

Hi all. I got my Arcana eARC box delivered today and have connected it to my Apple TV 4K and from there to my Samsung Q9F and Sonos Arc. I can confirm I am now getting Dolby Atmos.

Awesome! Welcome to the club!