Hi @TimShipston
Welcome to the Sonos Community!
I’m not sure why you came to the conclusion that Sky Q does not support Atmos - a quick search provided this page as the first result: https://www.sky.com/help/articles/setting-up-dolby-atmos. Please note, however, that for you to receive Atmos audio, the source content must be in Atmos, the source device must support Atmos, the TV must support Atmos, and the audio system must support Atmos. At present, only the TV and the source media are in question. Note that with an HDMI-ARC connection, only Dolby Digital + (Atmos) is supported, and not uncompressed Atmos MAT, which usually comes from BluRay or Apple TV devices and requires eARC.
As for why you’re not even able to get 5.1 audio, I would initially (until proven wrong) put this down to the TV’s settings and/or capabilities. Please look in your TV’s settings for an option labelled something along the lines of “audio output format” and set it to Auto, Passthrough, or Dolby Digital + (if it’s already set to one of these, try another). Note that some TVs only allow certain settings to be selectable if a source with surround sound is currently playing.
It may also help to look for a similar setting on your Sky Q box, and possibly even each of the apps you mention.
Please also bear in mind that some TV’s are limited as to what formats they will pass to an external audio device - if you let us know your TV model, we can look up the manual for you.
I hope this helps.
Thanks very much for the reply @Corry P 
My mistake on the Sky Q / Atmos front - I’d seen that same page you’ve linked to and was basing my assumption on this bit...
“Dolby Atmos is not available via TV apps on Sky Q, such as Disney+, Netflix etc. If you want to experience Dolby Atmos while using these, you'll need to switch to the app on your Smart TV.”
But I’m presuming that doesn’t apply to ‘native’ Sky Q content - i.e. live or recorded from Sky (or others) should be fine.
The TV is a Sony KD-49X8309C - it’s 10 years old this year, I think, so positively middle aged! 
I’ve had no further joy linking the TV’s arc socket with the Sonos ARC. but I’ve swapped over to the TV’s optical output and have now got most sources (TV apps, Sky Q apps, Apple TV apps) streaming in 5.1. Oddly, the only exception is Disney+ streamed via the TV app.
Hi @TimShipston
According to the TV’s manual, which does not mention Atmos in any way, the best audio you’ll get from that model is DTS, where available.
However, some older TVs were somewhat restrictive in what they would pass from an HDMI input to the HDMI-ARC output - some would only give you surround sound if you used a source internal to the TV. That you can only get 5.1 using a TV app suggests to me that your TV is one of them, though I do recommend contacting Sony just to make sure, as the manuals do not list what a device cannot do, only what they can do.
I’ve had no further joy linking the TV’s arc socket with the Sonos ARC. but I’ve swapped over to the TV’s optical output and have now got most sources (TV apps, Sky Q apps, Apple TV apps) streaming in 5.1. Oddly, the only exception is Disney+ streamed via the TV app.
This is good - there is no loss of quality when comparing HDMI-ARC to Optical (when the TV doesn’t support Atmos, that is). The only real differences are that a) you can no longer use the TV’s remote to control volume until you program the Arc to accept the remote’s commands (see our Control Sonos home theater with your TV remote help page for instructions) and b) you can’t use a voice assistant on the Arc to turn on/off the TV.
To experience the full capability of your Arc, however, you would either need to replace the TV with a model that supports Atmos, or add a (unsupported by Sonos) device into the chain like a HD Fury Arcana (not a recommendation!), though I think these days you could get a new TV for the same price.
Glad to hear you are getting surround sound now, though!
