That’s an excellent question. I am not sure how the speakers would react during setup to having two SonosNet signals to connect to. I think I’d be tempted to completely power down one system while setting up the other, and then do the same thing on the opposite side, powering down the ‘other’ system. But I’m not guaranteeing it will work, it’s just what I would try. 

And then come back and tell us what your experience was ;)

Thanks. Tried as you said. Turned off the S2 Boost, then turned on Bridge and set up an S1 system. Turned the S2 Boost back on and now have both an S1 and S2 system working within the same LAN.

Has taken a few days to get to this point. I hadn’t managed to find any information elsewhere that would help me in this situation. The new S1 app was unhelpful as it keeps referring to the Boost product when I was using a Bridge.

The apps refer to having a ‘Boost’ wired during setup because Bridge hasn’t been sold for over 5 years. It makes no difference. The app will detect the Bridge and act accordingly.

By the way, it shouldn’t be necessary to turn off an S2 system to set up a separate S1 system. The controller and players would figure it out, so long as the controller wasn’t already registered with the first system.

I'm thinking of it from a user experience point of view. When setting up your S1 network, the android app instructs the user to connect a Boost directly to your router. This has the potential to create confusion. If the app instructed the user to connect the Bridge or Boost that will be used exclusively for the S1 system then this unclear situation may be avoided.

Interestingly in my situation I wasn't able to just set up the S1 network with the S2 network powered on. I initially removed products that were not compatible with S2 via the S2 app. These were a Play 5 Gen1 and a Bridge. I subsequently set up a S2 network using a new Boost. I was then unable to set up a new S1 network using the Bridge.

Eventually I turned off the S2 Boost, factory reset the Bridge and was able to set up an S1 network. I'm not sure whether it was the factory reset or turning off the S2 Boost that helped.