Not really. Two options.

In the home theatre settings, under Surround audio / Music, move the music slider fully to the right. This will make the surrounds the dominant speakers when playing music (so the Beam will be way down in the volume mix), but will keep normal balance for TV. Make sure Music Playback is Full and not Ambient.
 

OR

Youll need to remove surrounds every time you play music and set them up as a stereo pair; and add them back in as surrounds for TV viewing. This is completely impractical.

Thanks for your reply.
 Hmmm, I still understood that there is no realistic way to switch between surround and stereo environments.
 I think it is technically possible to have two profiles set up and be able to switch between them.

No, you can’t switch between the two environments easily once surrounds are set up. When you add surrounds, the Beam bonds with them via its own wifi to ensure they can all communicate correctly and in sync. To play the surrounds as a stereo pair, you’d need to remove this bond by selecting “Remove Surrounds” and then set them up as a pair on your wifi.

Setting up different profiles won’t change the way the speakers are bonded. The Sonos app is in effect a remote control - the speakers themselves are connected in a certain way, to each other and/or the router, regardless of your Sonos app. I’m fairly sure you can’t operate the same system from two different profiles anyway.  

Thank you for your kind explanation.
I understand what you are saying, although I think I have been misunderstood.

By the way, it seems to me that what I want can be achieved if I can simply set the volume of the home theater speakers and surround speakers separately in a surround environment without having to go through all that trouble.
I just need to set the volume of the home theater speakers to zero.
I think it would be a good idea.
With the current specs,we can only control the volume of the surround speakers, right?
I guess Sonos basically wants us to use Trueplay and leave it to them.

If you do as I mentioned - in the settings, turn up the surround level under ‘Music’, with Music Playback on ‘Full’ - then whenever you play music, the surrounds will be the loudest speakers, with the soundbar much quieter. It will appear as if it’s only the surrounds playing the music, in stereo.

You won’t need to ever adjust this as it will automatically turn up the surrounds when you play music (you might need to tap the volume down a little when you do play music to avoid the surrounds coming up too loud).

> You won’t need to ever adjust this as it will automatically turn up the surrounds when you play music (you might need to tap the volume down a little when you do play music to avoid the surrounds coming up too loud).

You may think so, but I do not.
I don't want to hear everything in surround sound.
That is my value system, not yours to decide.

Thank you.

What an odd reply. I think you are seriously misunderstanding what I am saying!

I am helping you to set up your surrounds so that when you play music, the soundbar is minimised and your surrounds will sound like stereo speakers. This is the only solution to what you want to do. 

I have not voiced an opinion!

EDIT: I notice you are from Japan. There might have been a language issue which you might have translated inaccurately. I hope you can understand the instruction I have given in my previous replies. 

FIrst off, this is a user’s group and the person you are replying to doesn’t work for Sonos.  Second of all, what you want to hear doesn’t enter into it.  You cannot easily switch between surround and stereo from your rear speakers, no matter what you “want” or who decides what.  You just can’t do it.  So either you take the compromise given to you by the kind soul helping you out for free, or you need to purchase dedicated stereo speakers for those times when you wish to switch to listening in true stereo.