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Can’t you just use the Sonos Port’s digital coax output, to the coax input on those KEF speakers?

Have you tried connecting the Port from its Digital Out to the Coax input on the KEF using a digital coax cable?

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If you are still looking at RCA connections try any other line-level source connected to your speakers, if it works then the Port connected the same way should too.

You can test the RCA out on the Port by using a male RCA to female 3.5 mm stereo jack and a set of headphones. Volume will be low but you should hear sound. You can again check the setup by using your other line-level player to make sure the cable and headphones are good.

Thanks. I will try buying a coaxial cable and report the result. Realized that the KEF was in need of a firmware update and thought that was my problem. Unfortunately, all my attempts at a KEF update failed. I have reached out to their tech support. I bought the KEFs before Sonos began investing research into more high quality modern speakers. Sigh.

Hello. Bought a coaxial cable only to realize the Port doesn’t have a coaxial imput. Did I buy the wrong cable? The one I purchased is the standard coaxial cable that I have seen used on cable Internet boxes. Thanks.

You need a digital coaxial cable like this:

https://a.co/d/i1cI8VO

Apart from the fact that you’d want an output on the Port (which it has) it sounds like you don’t have a 75 ohm digital audio cable, with RCA terminations.

Yes, wrong. Cable just ordered the correct one. So much for ordering something on Amazon when tired. Thanks for your help!

Hi, My KEF speakers don’t appear to have a digital audio in slot. The subwoofer slot looks like it takes a digital audio connector, but I doubt that would work. Here is a photo of what is available. RCA has not been successful. Any other ideas? Thanks.

RCA to the AUX (C) inputs should work, unless the Port is faulty.

To use the Port’s digital out you’ll need a coax-to-optical converter (plus an optical cable). I don’t know your country but they cost £15 or less in the UK. You’d then connect to the Optical (B) socket.

The Subwoofer (S) socket is an output.

That Sub-woofer (S) plug looks to be a mono- RCA 

My KEF LS50s are now working with my Sonos system using the RCA plugs. The issue was sadly user error. It turned out that the Sonos Port required the volume on the KEFS to be turned up significantly higher than the previous Sonos Connect plus the volume button on the KEFs is no longer responding as it did. It flashes as if volume is maxed out, though it is not. I do have one lingering question. I was not able to install the longstanding driver update on the KEFs LS50s. The update failed and I couldn’t successfully reinstall the system software working with KEF support for nearly two hours. I am wondering if I am sacrificing sound quality running on the old drivers or if I should just leave well enough alone now that I have a functional system. Thanks for your advice.

The driver question might best be directed to a KEF forum.

Good to hear you have them working for you.