Is this possible to have a Single Sonos device in multiple configurations?

The Sonos app doesn’t allow it. Arc is front three channels and Eras are the surrounds I. Your 5.1 setup. You’d then have to “un-bond” the surrounds and set them up as a stereo pair identified by a new roomname. This will lose any Trueplay settings, and the whole process needs repeating to restore your 5.1 system. 
 

You can set the Eras to “Full” audio and adjust their volume relative to the Arc for music listening. That’s a compromise that a lot of owners seem to make. Or buy 2 more speakers for music listening. 

Hmmm.

Use ‘hobbled’ speakers for music listening or spend another £800 to listen to stereo music in my living room.

I did not expect using Sonos equipment would require me to make any compromises.

Let me check the returns details...

Don’t underestimate the quality of sound that can be achieved for music with a Sonos Sound Bar. I have two rooms with playbar/sun/surround combinations and find that listening to music in both is a great experience.

As @nik9669a says set music playback for the surrounds to full and set the volume to taste.

It’s important to understand what is at work here.  Wireless speakers  have far more complicated issues to overcome than traditional setups.  It all has to do with the connections between the speakers and the configuration required for Home Theater (which needs to be synched with the video) and multi-room audio (which needs to pass through walls, floors, etc.).  When adding surrounds/Subs, in order to maintain sync with the video, the radios are reconfigured to a low latency, one-way dedicated 5 GHz connection from the soundbar to the surrounds and sub(s).  This requires a series of handshakes to get right, which is why adding surrounds/Subs takes a bit of time. 

The reverse happens when the surrounds/Subs are removed.  So therefore, a quick toggle between the two is not possible.  They could place a hot button that does the add/remove at the touch of the button, but that is not going to speed up the actual process, and doesn’t save much from the system menu commands we have today.

As an aside, you aren’t going to find any competitors to Sonos who have solved this problem, and not many (sans Denon, who are paying Sonos for its patents) who even attempt to do wireless Home Theater.

I am not suggesting the Sonos products do not ‘play’ well, but as they artificially distribute a stereo sound to more than two ‘speakers’ the sound stage must be significantly altered. 

In a multi-room setup, that is fine… if I am wandering from room to room the ‘stereo experience’ doesn’t matter that much, but I cannot see how it is possible to sit down in the stereo ‘hotspot’ and to realise the music as it was intended to be heard.

My previous (perhaps current again) receiver / wired speaker system could detect the incoming signal type and adjust its treatment of it accordingly (i.e. a ‘spatial’ signal through every speaker and stereo through the front pair only).

I seem to have taken a few steps backwards in trying to move to a more modern system.  I was ‘umming and ahhing’ even about the Sonos set up having the stereo pair behind me, but was prepared to give it a go… cant do that now!

I’m not sure what this has to do with my explanation, but I’ll move past and instead give this information:  Sonos does have a “Full” and “Ambient” switch when playing music sources through surrounds.  “Full” will give full volume, instead of the default low volume.  The fronts will still play, which is not what you are requesting, but what you are requesting isn’t possible dueo the above configuration issues. 

Sorry for the confusion.  My reply was to the message before yours!

Also, to all the current and any future contributors thank you for taking the time to reply and I apologise if my tone of my posts seemed a little terse!  :)

This feature is sorely needed.   I don’t care if it takes a minute to make the switch, but it should save the trueplay and other settings and be easily done in the app.  

Thanks for weighing in on this…

I agree with your comment.  I didn't say at the time because I allowed my annoyance to come through in my posts at the time and I didn't want to annoy users or moderators.

It seems to me that the data created/recorded during initial and Trueplay setup is stored somewhere, it persists somewhere and is available after power cycling, so why can't 2 or more configurations be stored somewhere and restored based on user selection.  Clearly, if the speakers had been repositioned, existing data would be irrelevant and new measurements would be required.