Pro-Ject RPM 1.3 Gen, Pro-Ject Stereo Box S Phono + Play 5?

Sort of. That turntable has no phono pre-amp, which is required to turn the phono output into the line-level iutput required by the Play:5 line-in. The Pro-Ject Stereo Box S Phono is an amplifier as well as a phono pre-amp, but you will not need the amplifier section. You could connect the phono RCA out on the turntable to the phono in on the Pro-Ject Stereo Box S Phono, then use the line-output to the line-in on the Play:5. However, that's a pretty expensive way to get a pre-amp. Selling the Pro-Ject Stereo Box S Phono and buying a simple phono pre-amp would recoup a bunch of money. A phono pre-amp can be had for well under $50 US, even the Pro-ject model is < $100 US.

The Stereo S box is a great little amp and not one to discard, assuming you have some speakers hooked up and happy with the sound you could add a Sonos Connect. This would let you stream Apple Music / Spotify etc. to your existing system and in the future (if you purchase more Sonos gear) stream your records to other areas io the house.

If trying to downsize (pretty hard considering the size of Pro-ject gear) then go with what jgatie suggests.

jgatie. Thanks for the reply. Is having the amplifier section on the Stereo Box an added advantage or would it hinder the performance having it attached? The only reason I ask is that by the time I have try to sell it on Ebay or wherever and paid the fees etc the financial difference could be minimal.

Belly M. Again, thanks for the reply. I currently have some old floor standing speakers (which work really well) attached to it but will be getting rid of them as I am relocating my system and just going for the Sonos Player 5 as it would minimise my setup, and potentially if I could afford it, to add another Player 5 in the future.

So my system could be: Pro-Ject RPM 1.3 > Project Stereo Box S Phono > Sonos Player 5 (+Spotify/Apple Music). Could this work?

Not an advantage or a hindrance. Just not in the reproduction path any more. You could use it to power other speakers, but they would not be in sync with the Play:5 or others in the Sonos system.

Could be used as a switch if you had any other legacy equipment such as a tuner you wanted to stream to Sonos but if getting two Play 5's that gives you two line-in's anyway.