SONOS AMP is designed to drive passive speakers. Yes, there is an analog input and this input can be played in any combination of SONOS “Rooms”. Note that there will be a 75ms time offset between input from the CXA81 and output from the SONOS system. This is not likely an issue unless you are able to simultaneously hear a SONOS and CXA81 output at some locations.

SONOS PORT is similar to a tape deck, with an analog input and output. You could connect PORT to the CSX81 as if it is a 3-head cassette deck. If your CSX81 supports a “tape monitor” function, you can pretend that you are monitoring a 3-head recording session of the turntable and have time alignment of both SONOS and CSX81 speaker outputs.

Thanks for the reply!  Unfortunately the only out on the CXA81 is a preamp out.  

What’s a CXA81? Who makes it? Do you have a link to a manual that you’d be willing to share?

It’s a Cambridge Audio CXA81.  Here’s the manual. I’m really not sure it will work the way i’m thinking.

https://manuals.cambridgeaudio.com/en/node/182/pdf/a4

Rather unsurprisingly, I’m with @buzz here. You’d be better off with a Port than a Sonos Amp. With all the caveats that he mentioned. 

So Sonos Port hooked up to the preamp out.  I’ll have a delay between the two systems but could turn off the “analog” system and just play everything through the sonos and that should work?  Thank you both for your help!

-Josh

Yes, that will work. The delay might not be an issue. For example, if one system plays in the basement and the other plays in other areas and you cannot hear the basement from the other areas, no one will notice the delay.

Could you not put the Port between the preamp and the CXA81? This would probably sync the sound of the turntable with any other Sonos devices.

If the turntable is the only external analog device you want to connect (and it should be) then I would suggest wiring the turntable to rhe pre-amp to the Port to any analog input on the amp (e.g. CD).