My own choice would be to bond the Sub with the 2 x Fives (set in a vertical orientation for stereo channel separation), but the real answer here, has to be to try the Sub bonded to either of your Sonos ‘rooms’ and see which you prefer.

Speaker orientation guidelines

You can place a Sonos Five, Play:5 (gen2) or Play:3 in either a horizontal or vertical orientation.

A horizontal speaker will output stereo audio over a wide soundstage while a vertical speaker will output mono audio/single audio channel. When placing a single speaker, Sonos recommend using a horizontal orientation. 

When either horizontal or vertical, make sure all four rubber feet are sitting completely on the flat surface. 

I will just add to the above with this slight clarification…

A single vertical speaker will not play in stereo (it’s mono audio only), whereas a single horizontal will have a left/right channel. Two speakers paired in stereo will play in stereo regardless of orientation.

If using the Fives as a stereo pair, then orient vertically with tweeters on the inside for a sharper stereo image, or put the tweeters on the outside for a slightly wider, but possibly more diffuse soundstage.

Also FWIW…

I use a Sub with two Fives in the Living Room. My own preference has been to set the Fives in a vertical orientation, with the tweeters on the outside for a slightly wider/diffused soundstage.

The Sub gives that added depth that you might normally experience when close to the stage at a live concert. I find a Sub makes quite a huge difference to the immersive stereo soundstage experience.

Hope that helps.

My personal opinion is to bundle with Beam since it has a lack of lower bass punch.

FIVEs themselves give an awesome performance, no need to add extra bass unless you have a very larger room to fulfill.

i have an ARC and 2 FIVES and sub and I already did both scenarios in my place.

Thanks all, beam&sub plus stereo fives set-up. Can also run together when extra oomph needed :-)