You can only have two speakers in a stereo pair. I do not know if Sonos intends to do a 4 channel stereo (I believe it was called Quadraphonic) function in their ecosystem.

I would post a feature request for that and see what happens.

But for now, you can group tow stereo pairs in the same room. There may be a slight delay between sets though.

Quad sound is 4 discrete channels, rather than two pairs of stereo. But you can have two (or more) sets of speakers in the same physical room. Call them Room1, Room2, or whatever: the room name is just a label for identifying them. Get your source playing and then group the other “room(s)”. They will play in sync unless the source is a tv signal via a grouped Arc etc. 

Looking to add speakers to stereo hence more is better I have no interest in quad. 

More is not better.  The sound was mastered for two speakers or two Atmos speakers, depending on the source.

 It would fill a large room better if you have two pairs of stereo speakers placed at opposite ends of the room.  This would work well for a party, but I would un-group them and listen to only one stereo pair for serious listening.  There should be no delay playing music.

I’m being a bit pedantic.

”Quadraphonic”, often called “Quad”, is an old audio format using four speakers. Quad has been replaced by Dolby surround. Simply adding another pair of stereo speakers to a stereo system does not transform the system into Quad. Processing on the record and playback ends of the chain is required. Dolby recording and playback processing is different from Quad.

For a while there were Quadraphonic records requiring a specialized turntable and playback processor. Quadraphonic records would render in stereo when played on a standard turntable.