Use the Sonos Upgrade Program and use the upgrade credits to replace the pair of Play:5s with a pair of Fives. This is Sonos’ best-sounding setup for music (in stereo).

If you want to save a little more money, you could get a pair of used Play:5 (Gen 2)s instead. They sound exactly the same as a pair of Fives.

How does your system sound now? What characteristic would you improve? Have you heard a system that sounds better than your system? If so, how was that system better than your system? What models were included in that system?

I’d be awfully tempted to add a SUB, bonded to those PLAY:5s, but upgrading them first to Fives makes sense, too. 

In addition to this advice, I would say that you should look at what makes the biggest difference to the heard sound quality - the speakers and the sound they delivery where placed in the room.

It looks like you are playing vinyl via the Connect+ Marantz+Bose, but the speakers are not in the main listening area. My approach would be get a pair of quality speakers to replace the Bose, see how they sound in the living room, and if you prefer that sound to any you have today, replace the play 5 units with those, redeploying the 5 units to where you have the Bose just now.

If you can access the used market, passive speakers from HiFi brands can be even more value than bought new - and are likely to have long service life left in them. But buy only after testing the sound they deliver from where they will be placed.

I would do one more thing: keep an eye out for a valve amplifier to replace the Marantz receiver, assuming that the latter is only to be used for driving the passive speaker pair. 4 to 6 glowing valves will complete the look of vinyl because vinyl is as much about looks and feel as it is about anything else! And with Connect in the signal stream, you can still pipe the music to other rooms that have Sonos speakers in them.