Here’s a picture

A Hi Res picture(!) please. The labels for the jacks cannot be read on this one. Plus, a clear picture of the front panel also will help.

sorry how’s this..

and the front 

Perfect. The answer to your question is yes you can, using the Tape In/Out jacks. And I am pretty sure there is a source/monitor selector on the front panel that will also allow the Sonos speakers to be in sync with those being played via the speaker terminals on the Marantz.

Yes, there it is, the tape monitor button on the front panel!

And the amp is a keeper as long as there is someone that can give it the occasional service. Amps with these features are not common these days.

Thank you very much.  I wasn’t going to use anything other than the Sonos speakers, will that still work?  I have some old Wharfedales but no room really

Yes it will still work, with the Marantz speaker terminals left unwired. But instead of a Port you could spend a little more and get a Sonos 5 speaker and a cheap phono preamp that suits the turntable. The output of the preamp would be wired directly to the 5 input jack. This way you save the space taken up by the Marantz, and also get an additional speaker in the home, assuming you can use that extra. The turntable can be played on it, on other Sonos speakers, and even without having any sound coming from the 5 if there are times you want it to be silent.

That’s great info, thank you very much.

Why would you want to use the Marantz? Do you need it as a preamp for your turntable? Because then you would also need a preamp for the Five or Port.