In the product description it does say you pair the Sub Mini to a room speaker set, so that’s probably what you missed. You can unpair it from Beam and pair with Fives, and vice versa put it would get tedious after a while. 
 

It does also say it works better with the smaller speakers like One and Ray, and in smaller rooms. With your Fives and an open plan room I would think a full-size Sub would be more beneficial. 

Remember you are asking Sonos to do something (connecting a Sub to two different sets of speakers)  you would would also not get from another manufacturer……..

Agree with both of you. Should have thought/read a bit more before jumping in. It definitely adds more depth to the 5s.

This question gets asked a lot and wish Sonos would implement this. Every single home theater receiver built in the last 30 yrs  can do this , why not Sonos ?  IF Sonos releases a higher end speaker like the rumored optimo I will be highly hesitant to purchase .  it’s crazy that you can’t add a sub to a stereo pair to listen to music then switch to watching movies with the same sub

Why wouldn’t you compare the Beam to other soundbars, since it’s a soundbar and not a home theatre receiver?  Can you name a soundbar where the sub it uses is connected to a separate system at the same time?  I’m not aware of any, much less every single one.  The Beam plays TV sources like a soundbar and music like a soundbar.  Some people don’t like the way the Beam plays music, so they get a separate pair of speakers for music.

If your implying that Sonos should have a setup with seperate front LCR speakers and the 2 rear as well as sub, like a home theatre, then that makes a bit more sense.  They don’t have that configuration, but even if they didn’t I doubt you’d be able to use a single sub for this room and a different room at the same time.

You can’t switch between linking a sub to a pair of speakers and a soundbar.  Since Optimo would be a pair of speakers with atmos and presumably ( my assumption) a connection to the TV, I assume they will play TV and music audio at high quality, removing the desire to try and straddle a sub between 2 Sonos rooms.

There’s a reason why it takes time to configure a Sub for use with a soundbar.  For Home Theater, a Sub is configured as a direct private link via 5GHz to the soundbar.  This is a one way connection that requires reconfiguring the radios and several handshakes to set up.  Conversely, the reverse is also true when you wish to switch back to regular music speakers.  Basically, in order to switch between the two, you would need to remove it from one and add it to the other, which you can do right now via the system setup.  There is no way to instantly switch between the two due to this need for reconfiguration and handshaking.