Hi.  Let’s park Dolby Atmos for a moment and concentrate on 5.1 surround sound.  To get surround sound out of the Arc you need a source that is suitably formatted.  What sources are you playing?  Streaming services? OTA TV from an aerial?  External streamer like Amazon Fire Stick or internal TV app?

Hello,

thanks for getting back to me by the way!

im using a 4K Apple TV with Netflix premium account. Also making sure I’m looking out for the Dolby sign underneath what I’m watching to make sure it actually has Dolby but still nothing. 
 

when I go to Sonos app on the arc it says ‘pcm’ or something which I’m assuming isn’t correct. 

I don’t have Apple TV but what I guess you need is a source programme / fil that says  “DD5.1” or “Dolby Digital 5.1” or just “5.1”.  You don’t need Atmos capability on anything to get surround sound.  

Do you have a Netflix app on your TV you could play from?

Ok so I don’t need my tv so have Dolby atmos or anything capability because I’m running the arc so that will achieve that for me? I’m also using the optical adapter as the ‘arc’ port doesn’t seem to be working in the tv. Will that make a difference?

I’ll have a look later at the Apple TV settings too and update you!

thanks again

As you’re using an optical connection to the TV here, you need to goto the video and audio settings on the Apple TV and change format to ON and select Dolby Digital 5.1, which is the highest the optical connection will support. Set the optical port on the TV to pass-through or leave it on auto and see if that  works for you.

Would the arc hdmi port support higher than the optical?

am I loosing quality using the optical? 

It depends on the connected devices, but yes, possibly…

As a broad brush answer:

Using optical rather than HDMI means that you cannot send DD+ (a lossy format) or Dolby TrueHD (a lossless format) to the Arc.  Given that Dolby Atmos piggybacks on one or other of these, it follows that you cannot get Dolby Atmos over optical.

Note 1: it does not follow that if you use an HDMI cable you will get Dolby Atmos, or indeed better sound.  There are other requirements to be met to achieve that.

Note 2: Lossless audio is pretty much irrelevant for streaming so you aren’t really losing anything here.

Note 3: Essentially the Arc will play what it is sent.  The challenge is sending it the right thing.

Thanks for all the advise. I’ve changed the settings on the audio out on my Apple TV and it’s changed to 5.1! Sounds so much better all speakers working. Very happy. Thanks everyone!