At the time of the upgrade, you get to choose which devices to migrate to S2.  You can also factory reset an S2 device and then add it back to an S1 system.  

You’d need to factory reset a subset of your units (plus at least one controller) and set them up as a new system. The usual caveats about loss of settings/services/playlists apply. 

You may want to do this is on the ‘left behind’ legacy kit, setting up a separate S1 system. It can use the same email/account as before.

Russ_H

You can find a lot of information about S1/S2 mixed households here too: 

https://support.sonos.com/s/article/4786

https://support.sonos.com/s/article/4824

i’m curious on the above.  in this Sonos article on split S1/S2 systems they state the process of S1->S2 is not reversible:

Is this process reversible?

No, once products have upgraded to S2, they cannot be downgraded back to S1 or added to an S1 system. Make sure you want to create a split system before following this process.

am i missing something you’ve seen elsewhere?

People have confirmed they have done it.  Given the statement by Sonos, I wouldn’t count on that being the case forever,  

People have confirmed they have done it.  Given the statement by Sonos, I wouldn’t count on that being the case forever,  

do you have a link?  i have a situation where this may be needed. thx.

See this exchange: https://en.community.sonos.com/controllers-software-228995/sonos-s2-6842079?postid=16436406#post16436406

thx - i should have known to check ratty’s feed. :-)