Mixed mode question

I have a 6 zone system; 5 are in an open plan large space with an attached patio, in line of sight of the router and the boost that is wired to it. Of these, 3 are wired to the core network and therefore the boost, with Wifi disabled.

The 6th zone is in the bedroom, a play 1 stereo pair. It is separated from the open space by a brick wall, and is usually yellow and sometimes orange box in the Matrix. In this room, I have a Airport express unit that is ethernet wired back to the router, and it therefore provides a very strong WiFi signal in the bedroom. However, it is not convenient to run more wire to get the play 1 pair wire connected to the core network.

I do not want to disturb the set up in the open plan space for 5 zones; that is working flawlessly. The question is, can I make use of the strong WiFi signal in the bedroom for the 1 pair located there? Note that any additional bridge to give the 1 pair a better signal does not work; the bridge is ignored because the cost of the resultant two hops is more than that of the direct connection to the boost that is wired to the router.

If yes, what do I have to do to get the play 1 pair off Sonos net and on to the Bedroom AEX network that has its own SSID? Note also that the need to play this pair grouped with any of the other zones never arises.

Also, will this allow music to play on the 1 pair via things like Spotify Connect with boost powered off?