I’m not sure I understand what you’re saying here, ​@velvel. How can “purism” block the artist’s intent if the audio plays according to the source data? If the artist wants stereo from front and rear speakers they can mix it that way. If they only set a soundtrack to play to the front but the system plays to rears as well, then surely that is interfering with the artist’s intent? 

I do agree. It would be nice to have the option to play the left and right channels of Stereo PCM in the left and right surrounds too - basically in the same way Full and Ambient operates for music. 

(Where a music artist/producer mixes a song for stereo, it can be played ‘Full’ on Sonos, with the left and right replicated at the rears. The same process should be accessible for TV too. Neither case interferes with the creator’s intent.)

This happens with my Apple TV / Playbar / Play:3s. It takes DD 2.0 (from f1tv specifically) and extracts rear channels from it (engine noises, never speech). Works great.

​@controlav 

I get sound in the rears with 2.0 Multichannel PCM (on terrestrial broadcast football for example which extracts crowd noise to create a sort of surround), but Stereo PCM comes solely from the Arc. 

The ‘artist intent’ is far from the only factor.  If the source isn’t broadcast with stereo in the rear, or the TV is not capable, then you can’t get stereo in the rear despite the artist intent.  Personally, I don’t thnk artist intent should override listener preference.

To be fair though, I don’t recall Sonos ever stating they won’t play stereo in the rear for ‘artist intent’ reasons. They have stated they try to alter the audio to give their speakers a unique signature,  or provide sound profiles, etc, but nothing about stereo in the rear.  I don’t recall a good reason why the feature is there for music sources, but not for TV, other that consumers may get confused why they hear very little audio for surround/atmos sources when nothing is playing on those channels.

Could be! Consumers are confused enough by Sonos as it is! 

I should have said in my first reply: I, too, would like the option to select whether or not to hear the sound from rear speakers. I was just confused by, perhaps, the wording of the original post. 
 

Thanks everyone for the thoughtful comments.  Indeed,Sonos already offers this option in music mode: when I play stereo music via AirPlay/Spotify Connect, I can set surrounds to Full, and they simply mirror the L/R channels. Yet with HDMI stereo PCM, Sonos disables that exact same option. The Arc is clearly capable of putting signal in the rears.
So the real inconsistency is: why does Sonos allow this flexibility for music sources but forbid it for HDMI inputs? Unless there’s a genuine technical or licensing barrier, it feels like a restriction that neither artists nor customers asked for.

Though I’d like an option to play stereo on all speakers with TV sound (like full mode with non TV sources), I am puzzled by your frame that by not allowing this, Sonos is somehow sabotaging creative intent. If the creator wanted stereo, so front speakers only, his intent is clear: no rear speakers. By not allowing this Sonos is “respecting the mix”. Your request would be to not do what the creator intended by doubling the stereo mix to also include rears.

Your analogy also misses the point. A creator would want to show his work full screen on an HD TV, not showing it with edges. TV makers follow this wish on 4K TV’s by converting the picture to 4K.

 106Rallye:
 

There’s another side to this: if an artist did want their stereo mix mirrored into the rears, that possibility is entirely dependent on the playback system. In that case, it’s not the artist limiting intent, it’s the hardware.

And that’s where Sonos feels inconsistent. In music mode, the Arc already allows mirrored stereo with the Full option which gives users the choice. But in HDMI/TV mode, the same option is blocked

Unless it's a 5.1/Atmos etc. mix, there is no fwd/rear ‘intent’, it's a stereo mix,  which is left and right.  I don't understand the pushback mentioning a creator's stereo intent being front without rears.

People get this everyday without thinking about it - in their cars for example.  As a minimum, most cars have speakers in the front and probably the rear doors too, all in stereo.  Not having sound out of the rears (albeit the exact same sound as the fronts) would sound weird.

I will explore and attempt the FeinTech VAX04101A approach.  Lets hope Sonos decides to look into this though. 

So just to try to understand your issue:
Your source is only sending the audio to the two front channels, but sends nothing to the rear channels for the media you are playing.
You want the audio from the front channels duplicated to the rear channels.
Did I get this right?

I can see why this option isn’t available.
Because if your source is playing media it probably sends a signal containing audio to the front channels, but an empty signal to the rear channels.

So you want an option to overwrite the rear channels, but if you (or any other user) activates this and then plays an audio source which uses the rear channels, much more complaints of users having forgotten to deactivate the option, would be flooding support.

So all Sonos is doing is playing the audio in the same way it receives it.
So offering surround duplication only for pure stereo sources like music files or audio jacks makes sense.
They have no possibility to know if a surround source is generally just using the front channels or if they are just not used in the moment, but later on.