I’d think if it was possible, they’d have added it as a feature when they added the ability to have two subs in a Home Theater configuration.  And that requires a minimum of at least one of the Subs being a current version, where the other one can be of any generation. 

So, I wouldn’t expect it, no. 

You mean your 2.1 system and you want to take it to 2.2?

Note that it takes skill to set up a two Sub system because it is very easy for two Subs in one room to cancel each other out, leaving you in a worse place than that you are with 2.1.

In almost every domestic environment, for a Sub of Sonos quality, 2.2 is overkill for music play, even if properly set up.

Speaker placement can have a dramatic impact on the sound in a room. Have you tried the Sub in different locations, even just nearer/further from walls? Or it’s orientation - upright or on its “back”?

There is also a volume control, so you can increase the bass output relative to the volume from the Fives. 

I too have the same desire.  I had thought of configuring a second sub by combining it with the One's in another room and then taking the sub to the room where I have the two Five's + Sub.  Then I would synchronize the two rooms on the same source and I would finally have two Fives and two subs… The point is the second sub would probably have an equalization not suitable for the Five, being configured to couple with two small speakers.

@krismusic,

If not overly bothered with having stereo separation, you could simply attach a Sub to each standalone ‘Five’, perhaps orientated Horizontal, and then group the two (Sonos) ‘rooms’ together.