The ‘Full’ setting is for non-TV sources only, it has no impact on TV sources.  Sonos does not have an option for simulated surround sound, or to duplicate the front surround channels on the rear channels for TV sources.  Unless your Apple TV or other source has the option to send audio to rear channels for stereo sources, there isn’t anyway around this.

This is a fairly common feature request, and there hasn’t been any hint that it’s a feature Sonos is looking into.  Sonos rarely gives out hints to what they are working on, so that doesn’t really say much I suppose.

If you want music in your surrounds, you need to play music ‘Full’ from the Sonos app. 

Your TV treats music (e.g. Apple Music played on the Apple TV box) as a TV source (unless it is Spacial/Atmos), so just as stereo TV is primarily in the soundbar, the same applies to ‘TV’ music. 

It doesn’t.

Sadly. We purchased from Crutchfield which has 60 day returns so that’s one option.

That doesn’t seem to have any affect, which makes sense since it is just a “TV” source.

I don’t get what the issue is. If you want music in all speakers, play music via the app in ‘Full’.

Your system isn’t broken, it works as it is meant to. Your soundbar, sub and surrounds are a home theatre setup. It reproduces TV and movie content with sound going to the correct speaker channels.

Surround speakers are not intended to replicate stereo sound, no matter how much you wish that were the case.

It does if you play music via the app! 

Then you lose album cover art, and lyrics, on the TV screen.

I don’t know if this is clearer:

Apple Music on the TV:

• Playing stereo songs - the soundbar sees it as a stereo TV signal. So it plays in the soundbar and sub, and faintly in the surrounds. Treated exactly like a stereo TV signal.
• Playing Spacial songs - the soundbar sees it as a Dolby Atmos signal. So it plays in the soundbar, sub and surrounds. Treated exactly like a Dolby Atmos TV signal.

Apple Music as a music service in the Sonos app:

• Playing stereo songs - Sonos has a look at your settings:
  • If you have selected ‘Full’ in your surround settings for music, it will play the stereo song in soundbar, sub, and surrounds, with the surrounds replicating the soundbar’s stereo.
  • If you have selected ‘Ambient’, it will play stereo primarily in the soundbar, with a little ambient sound in the surrounds.

That is how it works. Through the TV, you can have the album art and lyrics, but you cannot make it operate in a way that it is not intended to. If you want all speakers, it must be through your app.

So that’s it. It is working as designed but not what I want. I’m looking into other options but returning the system is possible. 

I hope you can find something that does what you want. It feels extreme to take a brilliant piece of kit back because you want the lyrics on screen at the same time as sound from the rears but yours is a very specific and idiosyncratic use case.

The lyrics are just an example. I don’t want to be told how I can source my music. Steve Jobs once told people “You’re holding it wrong,” and that was wrong of him. Sonos is telling me how I must source my music. That’s not cool.

But man, the stuff does sound great when played the way Sonos wants me to play it. :- )

The Arc (or any home theatre system) can only process the signal it’s sent. If it’s from the tv it’s looking to see if it’s stereo, DD, etc. When it’s some form of 5.1 signal, it will send the received audio data to the relevant speaker. Music channels are typically only broadcast in stereo, so there is nothing to send to the rear speakers and this is why they remain silent.
I don’t know that any system can magic up some data to play in this situation, so I don’t know what you’ll find to replace your current kit with. I’m sure it’s a case of “they all do that”.

But it can magic up some data. It is easy. Left rear gets the same as left front, same for right rear. Or left rear gets right front, so you have a cross effect. (I run 4 speakers in my basement workshop that way, it it is pleasant enough unless you’re listening to classical music and then the violins are wrong.)

This isn’t rocket science, I don’t understand why it isn’t done. 

So play music like you do in your basement workshop. That’s not from a TV. 
I don’t get your resistance to playing Apple Music from the Sonos app - which is what Sonos was originally created to do - to achieve exactly what you describe above (left rear gets the same as left front, right rear gets the same as right front). I know you don’t want to be told how to play music, but play music on your Sonos app and you get incredible sound without having to take it all back. 
Anyway, I’ve explained in great detail how you can achieve what you want to, and how you can get the best of both worlds for TV and for music, just by using Sonos the way it was designed to work. You’ll be pleased to hear I’m done here.

I have the same concern also.

Use case: I would like to play music from the music app or YouTube app, initiated from my AppleTV 4K connected to my TV, and make use of every Sonos speaker. This is especially important for playing music videos on the TV! And also for playing music from Apple Music with cover art, making use of my TV as part of the experience. (With Lifx, Nanoleaf and Philips Hue lights completing the experience)

Intended behaviour: For stereo songs, there is Stereo sound from the Sonos setup. In this way, it is not behaving as a surrond sound setup, but as a collection of speakers to play stereo music from all L and R channels (rear and front). 

Possible solutions:

• each music app synthetically create a 5.1 output to the speakers, with the rear channels a duplicate of the front channels to emulate stereo. This would have to be implemented by each app.
• Airplay from the music app to the Sonos setup to bypass the TV altogether.
• Sonos app has a setting to ignore the rear speaker output and duplicate the front speakers.

The latter would result in the most consistent music-listening experience and is what we would like to see added to the Sonos app.

To play music from the Sonos app is an inferior solution from my iPhone. It does not put play controls on the lock screen of my iPhone so requires opening the app every time I want to change the song or adjust the volume. I cannot initiate with Siri. And the Apple Music interface is different to the music app. But importantly, I can only play the music on the sonos setup, ignoring HomePods.

By using Apple Music, Airplay makes it possible to play the same song simultaneously and in sync on any combination of Sonos or Aiplry speakers. This includes homepods and even my MacBook Pro speakers. This is the ultimate whole-home music experience where the music seamlessly blends between rooms.