I’m not quite sure what you are requesting here. These options are currently available for music playback on a Sonos Home Theatre setup :

1. Ambient Mode - Subtle, low volume audio from surrounds with a limited frequency range. This is the default setting for surround speakers during music playback.
2. Full Mode - Full range audio for surrounds at the same volume as the home theater speaker
3. Main Home Theatre device only (Arc/Beam etc.) - No audio from surrounds, which you may toggle ‘off’ in room settings .

All options are available in the main home theatre products ‘room’ settings (Surround Audio) in the Sonos App.

Exactly.

The problem is, if I want to listen my music only in stereo, I have to:

• Go to settings
• Choose System
• Choose my room
• Go to the Surround audio menu in the Sound section
• And toogle off Surrounds

And when I want to watch a movie or series in 5.1, I have to:

• Go to settings
• Choose System
• Choose my room
• Go to the Surround audio menu in the Sound section
• And toogle on Surrounds

And again the same manipulations if I want to listen to music in stereo after that.

Lots of manipulations for just listen the music in its original format (PCM 2.0) when you don't want a surround upmix.

And we lose the immediate and easy side that Sonos normally offers.

What I want, and what my old amplifiers did very well, is to have stereo sound when i’m listening a music source in PCM 2.0 ; and have 5.1 sound when the sound bar receives such a format.

For me it would be easier to have an option like « Original format » in Music playback submenu in the Surround audio settings so that the setting is done once for all.

Edit : And sorry for my poor English :/

Ah I see (I think) .. I don’t bother personally speaking, I just leave my HT setup set to ‘full’ for music playback and leave it at that. I assume the ‘majority’ of users however prefer ‘ambient’ which is the Sonos chosen default setting.
 

I assume that if the way you like to use your system became the popular ‘norm’ usage option, Sonos would perhaps then develop things to work in that way for its customers, but as a regular visitor to this forum, I’ve not seen much call for it to work in the way you have described.

So you only want stereo from your Arc? Is the ambient setting for the surrounds really that loud (I use Full myself, with a Beam)?

You can at least minimise it using the volume slider. Look under Settings, System, roomname, Surround Audio. That way, music is quietened but for tv it remains loud(er). Not ideal, but maybe worth a try since you don’t then have to keep turning the surrounds on and off?

Yes, Ambient or Full mode produces a rather unpleasant echo for me. 

And even the volume slider at minus 15, this echo effect is still noticeable.

Too bad that Sonos doesn’t do like other manufacturers and impose the surround mode. 

It is especially penalizing for me because, it is necessary to go through no less than 4 sub menus before having the option. 

For once, I almost regret having added surround speakers to my Sonos Arc 

I’ve never experienced an echo in any mode - are you sure you have the surrounds ‘bonded’ and not ‘grouped’ with other rooms ?  I would try Trueplay tuning the room again, if there is any kind of echo for your chosen listening position.

I agree. For surround there shouldn't be an acho.

Bless you. 

Sorry, I misspoke.

Strictly speaking, it is not an echo effect, but an unpleasant impression for me.
After several tests it is clear that the stereo sound is much more detailed than the sound with surrounds speakers.
I never would have thought that it would have been so difficult to have stereo sound after adding surround speakers.

For me it is such a basic function.

The way people perceive sound is very personal. What you are getting when playing music is double stereo (from the soundbar and from the surounds). I like it, but you don’t. As sketched above there’s no easy work around for this.

It would be handy if the surround mode [ambient, full, none] was settable for both music and TV and the individual setting was retained for each source. 

Actually it would be great if all the sound settings were kept for both music and TV modes so you could set each as you like and then just switch settings along with the source.

Same for me. Stereo PCM 2.0 should be always Stereo PCM 2.0 (+sub). But this is not working in that way. If you listening Stereo PCM 2.0 from HDMI (TV), Sonos will always “upmix” sound to 5.1. Awful. There should be option to disable that upmix. 
 

When listening thru Sonos app or airplay Sonos offer Full or Ambient options but it should be another option “off” without switching off Surround speakers in room.