You can use an RCA-Y cable to share the turntable output. Note, however, there will be a 75ms time offset between SONOS and your traditional setup.

You will want to use the turntable's internal phono-preamp and connect it to a Line-In connector (not the Phono) on your traditional setup.

You don't want two phono amplification/equalization stages in the signal path.

Just a slight correction regarding using the Pro-Ject Debut Carbon Turntable’s internal Pre-Amp. I have the same turntable in Black. The Internal Pre-Amp can be disabled to allow you to use the Phono-Amp input on your traditional setup. I have the internal pre-amp disabled in favor of a Cambridge Alva Duo pre-amp.

I would purchase a Sonos Port and connect it to Tape-in/Tape-out to send turntable music to other Sonos speakers. 

Yes that will work if not using a Y cable, with the Y, the internal preamp (or an external one) is needed as Sonos doesn't offer a phono level input.

Aside from that, splitting the phono level connection will present a load to the cartridge that may be a problem.

Thanks. I have an old port set up linked to a CD player in my studio. I’ll give that a try as well.

A question on the Pro-Ject Debut Carbon’s pre amp. To disable the pre-amp is that provided for with a switch or is it more complicated than that? Thanks

See the switch location in the picture and explanation:

Thanks! Very helpful and a different response from the SONOS on-line chat support.

You might consider one of the Victrola Stream models. I added an Onyx to my setup and streaming over WiFi actually sounds better than a wired connection to an amp/speakers. I think that’s mainly due to having the surrounds in my setup set to full (vice ambient), which makes 2-channel sound more immersive. I also have really good WiFi so I assume it’s achieving FLAC. I additionally have the Onyx paired to my Ace and that’s a pleasant listening experience, as well. They both have Bluetooth 5.4 for lossless audio.

I have the Onyx as well, and it works great, both using my speakers and bluetooth to my ACE.  I agree with you about streaming over WIFI vs Line in to my Port.  Wifi streaming sounds much better, probably due to the quality of the pre amp in the Onyx.  I would like to add an external pre amp, but the native one in the Onyx can’t be bypassed to my knowledge.

Personally, I prefer ripping the records, then playing the file. During a batch ripping process you can properly clean each record, custom adjust the vertical tracking angle, and, if you want to be completely anal, custom adjust the lateral cartridge alignment for each track. This is typically more work than desired for routine play, but it only needs to be done once. Another benefit is that progressive record wear (with.each play) is avoided. Record play is even sensitive to room temperature.