In the horizontal orientation the FIVE is actually a stereo speaker, but you need to almost push your nose to the speaker grill to realize this. Yes two FIVE’s could be used as the surround speakers and you could add a SUB or two to the surround system. Surround speakers become part of the surround “Room” and cannot be controlled separately.

If you configure two FIVE’s or ONE’s as a stereo pair, they become a “Room” any combination of Rooms can be “Grouped”.to play the same music. You can attach your turntable to a single or paired FIVE and stereo will be sent to any Grouped speakers.

You could purchase two Sonos Ones (or One SLs) and group them with the Five in the Sonos app to play music through all three speakers. If the two Ones are set up as a stereo pair they will play in stereo while they are grouped with the Five.

You can add a pair of Ones, One SLs, or Fives as surrounds to the Beam, but if they are set up as surround speakers, they cannot be used alone without also playing audio through the Beam. Also, the line-in port on the Five is disabled when it is set up as a surround speaker.

If surround sound for a home theater is important to you, I suggest getting a pair of One SLs to add as surrounds to the Beam and keep using the Five as your primary turntable speaker. Then you will have the option to group the Beam/One SLs setup to the Five to play audio out of all four speakers.

FYI… stereo music from the Beam plays in stereo, not mono. Also, if you group the Five with the Beam setup while playing TV audio, you will experience a slight audio delay from the Five. Music will be in sync though.

Thanks legends.. great responses ! 
so to get my head right - my preference would to be buy 2 ONES, have them toward the of the room for surround - link the ONES to the beam bar to create surround and that’s a room.

then, have the record player plugged into the FIVE, play it direct through that which is its own room - but if I wanted I could play music including records to both rooms - and that would send music to the beam and the pair of ones - and that would also still be in stereo - which means the pair of ONES which would be several metres apart could open the sound a bit ?? Does that sound right or have I misunderstood ??

That sounds right.

To save money, get the One SLs instead of the Ones. You will not be able to use the microphones/voice assistant on the Ones when they are set up as surround speakers for the Beam.

Also be sure to set the Music Playback setting under Surround Audio to Full instead of Ambient.

Note that while “Bonded” as part of a surround Room, you cannot play only the ONE’s, but they will play music in stereo -- along with BEAM. If you want to play only the ONE’s, you would need to first remove the ONE’s form the surround Room and bond them as a stereo pair, then add them again when you want surround. While this is not technically difficult, it would quickly become an unwelcome chore.