Can I use the SUB in 2 different configurations?

It's possible, but requires a lot of effort. Basically, each time you switch configurations, you would have to un-bond the SUB from one configuration, then bond it to the other (and perhaps TruePlay it, if you do that) each time. Sonos hasn't made this an easy thing to do, perhaps as a method of generating additional SUB sales. To be honest, I thought I might do something similar, until I set it up the first time. Now I just use the 5.1 system to listen to music, which has the SUB attached, and I put the extra pair of speakers in my bedroom. I set the Surrounds ( two Play:1s) to Full in the room settings, rather than Ambient, and it sounds pretty good.

You can certainly try, there's no penalty other than a bunch of key presses in the controller app every time you want to switch back and forth, but it isn't a simple "switch" operation.

I had the same idea when planning my next purchase. Now i"m planning on doing the same as Airgetlam.
Would have also liked to be able to mute the bar/base in a 5.1 setup which also isnt possible :(
Now the only item i am yet to confirm are the benefits of a 5 over a 1 in a 5.1 setup used equally for tv viewing music.

Not much for tv i would guess. Not sure about music though.

I had the same idea when planning my next purchase. Now i"m planning on doing the same as Airgetlam.
Would have also liked to be able to mute the bar/base in a 5.1 setup which also isnt possible :(
Now the only item i am yet to confirm are the benefits of a 5 over a 1 in a 5.1 setup used equally for tv viewing music.

Not much for tv i would guess. Not sure about music though.

From what I have read in another thread, I can safely use the PLAY 5 as surround (though it is really not a use of their potential). I found a good deal on a PLAYBASE+SUB combo on eBay and went ahead and purchased it (without the PLAY 1s).
So I will use the PLAY 5 as surround, but there is an option to use them as FULL, and this helps during music playback. I may also just keep it on each side of the TV (instead of keeping them at the back). Let's see how it goes.

Note that keeping the Play:5 in the front would ruin any surround sound effects, causing your TV audio to sound like a muddy mess.

Note that keeping the Play:5 in the front would ruin any surround sound effects, causing your TV audio to sound like a muddy mess.

Thanks. I will keep that in mind. On another discussion, one user (Lui) posted this, so I thought I will give it a try too:

"You could set up the play5s as surround speakers but place them left and right from the TV. Then in the surround settings you can set the music playback to full. You then can adjust the volume of the “surround” speakers, which are now actually front speakers, to your liking. I have set them to about 2/3 so that I get more and wider stereo sound from my play1s with a bit of sound added in from the playbar (and a lot of rumble for the sub btw … I just love that thing! 🙂 )."
https://en.community.sonos.com/home-theater-228993/two-play-5-as-front-speakers-with-playbar-center-6733469

I connected the SUB to the PLAY:5 stereo pair to see how it will sound. The PLAY:5 stereo set, on its own, is fabulous for music listening. Adding the SUB to this mix directs the low-frequencies to the SUB, and you can feel the obvious difference. But honestly, for music listening, I think I prefer the PLAY:5 pair without the SUB.

i I think I prefer the PLAY:5 pair without the SUB.
Fair preference, but try it once with the Sub after Trueplay if you haven't done this already.

It's such a subjective thing, I'd have to do the testing, as Kumar suggests, before drawing my own conclusion. I suspect there are a lot of factors involved in the decision, room size, furniture, music type, personal preferences, etc. What works for Kumar may or may not work for me, which is why his suggestion, since you already have the equipment, is the best idea possible.

I finally ended up using the 2 PLAY:5 as surrounds. They are underutilized for normal 5.1 listening, but when playing music with playback set to 'full', the setup sounds awesome.