Before spending the money on an additional BOOST (which isn’t much, mind you, but still), I’d try also wiring the Port, and see if that makes a difference in your situation. I’d also review the wifi interference FAQ, just using the channels listed is no guaranty that there’s nothing else there, or that you may have interference coming from other devices, inside or outside your home. 

Any device also wired helps the SonosNet network. 

Edit: Assuming that the wifi/radio isn’t turned off on that Sonos device.

Thank your for your quick reply

Any device also wired helps the SonosNet network. 

Can you explain what the relationship between the SonosNet network and wired Sonos artifacts is? Will they genereate a more ‘powerfull’ wireless Sonetnet network when wired?

Assuming that the wifi/radio isn’t turned off on that Sonos device.

Correct assumption :-)

It’s one of the early mesh networks, before they became common. So each wired device becomes a wired source of the signal, which can help reinforce the mesh. But if you have a device that isn’t within SonosNet or WiFi distance, any number of wired devices won’t help. Too far is too far, whether you’re using SonosNet or traditional WiFi. For practical purposes, SonosNet is the same as any radio or WiFi signal, subject to the same physics. 

 So each wired device becomes a wired source of the signal, which can help reinforce the mesh.

Is above also applicable for the PORT signal? So when spinning vinyl. How will this work as this signal is not coming from outside (internet)

Sorry for the questions and thanks for the answers upfront

The Port will be the entry point for the sound from the record player and will pass this to the other devices (when told to do so). That's why it's called a Port…...

That I do understand. But it will pass it on wireless, I assume. So why should the PORT be wired?
That's my question…. If the signal is not coming from the internet (eg. Spotify), why should the PORT be wired?

When playing material from connected sources the Port will probably pass it on wirelessly to devices connected wireleslybut also by cable to other cable connected points.