In the Sonos App, go to System > System Settings > About My System and scroll down to the Sonos Arc information and look at “Audio In:” This will tell you exactly what type of audio the Arc is playing. 
 

FYI, you can’t get Dolby Atmos audio from YouTube videos.

I’m having this same problem with my Xbox Series X. I’ve got the Arc, 2x Gen 3 sub’s & 2x One’s and whatever I watch it’s stuck on Dolby Atmos in the main screens and within settings even when watching YouTube and I’ve checked the rears; nothing is coming out, is this a bug?

The Xbox or TV is probably upmixing the audio to Dolby Atmos. What are your audio settings on your TV and Xbox set to?

Hi Guitar,

Firstly, thanks for replying so quickly! My TV is an Aldi TV with just an ARC port which doesn’t give me a eArc signal so I bought a HDFury Arcana dongle which like you said previously upscale the signal; my Xbox is connected directly into the Arcana which for some reason just upscale literally everything to Dolby Atmos but on Xbox I have the following setting:

Speaker Audio Option:

• I’m using the following setting “Bitstream Out” out of the following options: Off, Stereo Uncompressed, 5.1 uncompressed & 7.1 uncompressed.
• in the Bitstream Format settings I selected “Dolby Atmos for home theatre” and these were other options: DTS Surround, Dolby Digital & DTS:X for home theatre (HDMI).

If I chose Dolby Digital within the Bitstream Format, it says Dolby Digital 5.1 when watching Atmos content on Disney+; whereas when if I’m using Dolby Atmos, it upscale a everything even YouTube to Atmos and it never goes away.

The Arcana doesn’t upscale the audio signal. It just allows any external media device to bypass your TV and send audio directly to the Arc.

From what I can tell, the Xbox just upmixes everything up to Dolby Atmos when you have “Dolby Atmos for Home Theater” selected.

I found this on another website about the Xbox:

When using “Dolby Atmos for Home Theater” audio settings:
Streams non-Dolby Atmos content (e.g 5.1 channels) on Netflix, Amazon Prime or Vudu apps, Xbox One console will cause the console to send out blank Surround Left and Right audio channels, causing missing audio on the Surround Left and Right channels of the soundbar.

Solution:
When streaming 5.1 non-Dolby Atmos content on Netflix, Amazon Prime or Vudu apps, change the audio bitstream output to Dolby Digital to experience surround sound from all channels.

https://www.helpdesk.nakamichi-usa.com/xbox-series-x-audio

That’s amazing, thank you! So, I’m other words, every time I’m going to need to change it to either get 5.1 or Atmos; am I understanding it correctly?

Also, if I bought a TV with an earc port, would I still have this problem?

So, I’m other words, every time I’m going to need to change it to either get 5.1 or Atmos; am I understanding it correctly?

Yes, it seems so. If this bothers you, you should consider getting an Apple TV 4K or Roku Ultra.

Also, if I bought a TV with an earc port, would I still have this problem?

Yes. The Arcana is basically a TV with an eARC port without the TV screen.

GuitarSuperstar, you are the best. So now I’m asking would I notice any major improvement by adding an Arcana to my Sony tv that has only an Arc output? It has 3 inputs plus Android tv. I have an Apple TV 4K, a Firestick 4K, and a Roku Ultra 2020 plugged in.

@toyboy Are you currently getting Dolby Atmos audio playing out of the Arc from those three devices?

With Netflix only the Roku Ultra 2020. 

For those who have the Xbox one s,x or series Xbox’s if you have set up to play Dolby atmos it will up mix everything to atmos, I noticed this when I was watching terminator 2 in dishd on my Sonos app it was showing as atmos.

With the Arcana, you will be able to get Dolby Atmos audio from your Apple TV 4K and Firestick 4K too. NOTE: The Arcana won’t make any difference with your TV’s internal apps.
 

FYI… with the latest Roku Ultra, you should currently be able to get Dolby Atmos audio from Disney+, Prime Video, VUDU, and Apple TV+ too.

Do you like that the Xbox upmixes everything? Does it sound ok? Can this be disabled?

It sounds good, I was watching EXODUS on dtshd it was awesome, you can disable it by setting the audio options LPCM 5.1 or 7.1.

I forgot my Android TV does do Dolby Atmos for both Netflix and Prime Video. I just doesn’t do Atomos for Netflix on Fire Stick 4K nor Apple TV 4K. I do get Apple+ in Dolby Atmos on Roku Ultra 2020.

@toyboy Since you are able to get Dolby Atmos from most of the major streaming apps, you really don’t need to add the Arcana unless you want every app on every device to function at its full potential, you plan on adding a Blu-ray or UHD player to your setup, or you are experiencing lip sync issues.

For reference when using the arcana to upmix all audio to Atmos, it does help if you cannot or your tv will not give you 5.1 and it’s extremely easy to setup. In order to get the Xbox to recognise Atmos, you will need an Arcana as it still has to upmix the audio to your Sonos system. 
 

Although, it is weird that the Sonos app cannot switch it on and off as required e.g. when watching YouTube and YouTube cannot support Atmos. Apple Tv does toggle it on and off depending on the app you are using. I just wasn’t sure this was normal but apparently this is a normal occurrence with the Xbox that it upscales but you’ve got to download the Dolby app; just wish Sonos would support DTS though…. maybe one day....

I think I’ll take your advice and save the money. No Blu-ray player or UHD player planned and no lip-sync issues. Thank you for your valued advice.

Sonos is probably not going support DTS audio anytime soon, but the Arc does support multichannel LPCM. On your Blu-ray player, set your audio settings to convert DTS to PCM and you will get multichannel PCM from all of your DTS-encoded discs.

For clarity, arcana doesn’t upmix audio,  it’s job is essentially informing the source device what the audio capabilities of the Arc is so that the source can send the best possible audio format.  It is the xbox, or other source, that is upmixing audio, if any upmixing is occuring.

Arcana can do some video processing, depending on your source and TV capabilities, but that’s not really related.

I used to used internal TV apps and firetv for streaming.  Once I got an Android TV streamer (nvidia shield), which seems to stream everything without any restrictions, I have not use the internal apps of firetv.