The Sonos ceiling speakers are passive. Think "bookshelf speakers that need an amplifier". That's in essence what the £600rrp Sonos speakers are but mounted in the ceiling. You will need the speakers themselves, then speaker cables running in the ceiling void and down the wall to some accessible point. These cables will then be connected to an amplifier of some description. This could be the £700rrp Sonos
amp, or any third party amplifier you might already own.
The Sonos amp has a line level input on stereo RCA (phonos) but doesn't have a built-in phono pre-amp. This means that the signal from the turntable must be equalised and boosted before it reaches the Sonos amp. Fortunately a lot of turntables come with a built-in phono pre-amp for just this purpose. Those that haven't can be used with a standalone pre-amp that does the same job.
The £600 Sonos speakers alone are useless by themselves. They won't do anything unless powered via an amp. Personally I think they're also very expensive for what they are. Aside from the pivoting bass driver and the enclosure which removes the need and cost for fire hoods, there's not a lot here that you wouldn't get a a decent 6"-6.5" in-ceiling speaker from Blu-cube for half the price. The company that makes them is called Sonance. It is a US firm that has been around far longer than Sonos, and doing multiroom audio product for longer too.
Where there is a distinct advantage with the Sonos speaker is with the Sonos Truplay app. This is their room EQ feature. It's standard on a lot of the active speakers, and the Sonos Amp has it too, but... here's the catch... Truplay only works with speakers it already knows. Unlike AV receivers which also do room EQ, and they work with any brand and model of speaker, if you want Truplay to work then you're forced to buy the Sonos in-ceiling speakers.