You can’t without actually reconfiguring each room in the setup by removing surrounds/sub, then pairing them as a stereo pair and re-adding the Sub.  In other words, it can’t be done easily, it requires a complete reconfiguration of the radios which the current configuration steps are meant to handle. 

Also if using TruePlay you’d have to redo it after every configuration change.

Thank you for the response.  Its ashame I can not use multiple groups within the same room. i have 2 full arc based surround setups in my home, plus a half a dozen roams and one’s mixed thought out the house. I guess you can say I am all in on sonos. The config in the den is arc+era300’s+two sub. maybe in the future this can be an enhancement to sonos software?

Never say never, but it’s important to understand what is at work here.  When adding surrounds/Subs, the radios are reconfigured to a one-way dedicated 5 GHz connection from the soundbar to the surrounds and Subs.  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.

An alternative would be allowing one to mute the front device and just play out of the surrounds, which would appear to be easier to do, but I defer to the actual engineers on the practicality of the idea, especially with regards to spatial audio through Era 300s.   I’m sure switching from sending just surround info to sending a full Atmos audio stream through the Era 300 surrounds from the soundbar isn’t trivial, and given hardware limitations of the decoder and the way it is wired to the soundbar, may not even be possible.  Maybe in the Arc 2, perhaps ?