Not sure I understand your first comment? In what way is the Ray ‘less powerful’ than the five? It’s certainly designed for a different use case, but I’m not sure there is a true ‘apples to apples’ comparison available.

A few comments, though, before I move on to your next question. Surround speakers are designed to be placed ‘behind’ the listener, not flanking the front channels. The Ray contains the front left, front center, and front right signals. If I’m interpreting your post properly, you have rear right and rear left placed in front of you. 

I’ve got a pair of Fives flanking my TV set as well, but they are set up as a different ‘room’ for music listening only. I use a pair of PLAY:1s as surrounds, the sit behind me and are actively used when watching TV, but not usually for music. Although when I do use the home theater ‘room’ for music streaming, I’ve set the Sonos to use the surround speakers as ‘full’ in the controller’s settings, rather than ‘ambient’, so they act as regular stereo speakers in their own right.

Now, to your second question. Not really, Sonos allows any speaker to be part of one ‘room’ at a time. Yes, you can go through the process of changing setup with a few button presses, but it quickly becomes tedious, and you lose any truePlay settings you may hav generated for the room. I’d recommend going the extra mile and just getting the pair of Sonos One SLs to be surrounds, and keep the Fives as a separate ‘room’ just for music streaming. 

Thanks a lot for your answer !!

I think the good choice is : 

“I’d recommend going the extra mile and just getting the pair of Sonos One SLs to be surrounds, and keep the Fives as a separate ‘room’ just for music streaming.”