You have to remove the Sub from the Fives each time, then add them to the Beam. This will also cause you to lose any Trueplay tuning.

No it’s not possible to use/bond one Sub with both rooms at the same time - you could of course Group the rooms to bring the Sub into the mix when playing music and just have it bonded to your Beam instead, or perhaps consider purchasing another Sub/Sub-Mini - I have two Subs in my lounge for this very reason and I think a few others here in the community have done the same.

How annoying! If I got a mini would that be better for Music or TV? Or regular SUB for TV ?

In my opinion TV surround should be bigger than life. SUB can hit harder and is better suited in this context. I have dual SUB’s in my ARC based surround system. Dual SUB’s is lots of fun for TV.

I understand why you might prefer FIVE’s for music. Grouping the FIVE’s with the surround system, simply to bring SUB into the act is not everyone’s idea of great sound. You can reduce the rear level while playing music, but BEAM will still be playing. You could tinker with things by boosting SUB’s level while reducing BEAM’s output when listening to music. This level of tinkering consumes less elapsed time than removing SUB from BEAM and assigning it to the FIVES, but I’m sure either approach will become an unwelcome task over time.

If you are an over the top bass freak, I don’t think MINI will do the job. For many regular folk, FIVE’s have enough bass without SUB. Regardless of which subwoover you use, offloading the bass from the FIVE’s will improve the midrange.

In the end only you know what sounds “best” (to you).

The Sub is configured differently when it is bonded as part of a HT system, compared with when paired to music speakers.  It isn’t just like grouping and ungrouping speakers.  No doubt Sonos want to sell more Subs, but there is more to it than that.