You can’t set them as a stereo pair but you can group them as two mono speakers playing the same source. 

Is the play 3 not stereo

Apologies: I was trying to emphasise “not a stereo pair” with one as left channel and one as the right. 

Is there an alternative to the Sonos one gen 2 as I don’t want to get rid of the play 3

@Onion, You can set up as many Sonos units in the same physical room as you wish, if you got the space, and playing in sync by grouping them together. (Sonos “rooms” are virtual ones.)

@Onion . I think you may have misunderstood.  The two speakers can be played in sync without difficulty. They are fully compatible with each other. You just cannot use the two as a stereo pair (and hopefully you wouldn't want to).

Cheers