Maybe see the suggestions in this older community thread..

Unfortunately not . It doesn’t really offer a solution. The Starlink router is pretty locked down so there are minimal settings to amend 

Can you not cascade another router off it and use ‘double NAT’ and configure that router to use with the Sonos setup instead.

Depends on the StarLink in use. The ‘standard’ device has no Ethernet port on which you could cascade your own router. I’ve not tried it, but certainly would expect a travel router to be successful. 

I have a TP Link router that I could try via the Ethernet adapter on Starlink and stick it in bridge mode. I did try this before but it appears to really hinder download speeds. 
 
I also need more than 4 ports so need to connect a switch. Any ideas on the topology?

Thanks

There’s no need to ‘bridge’ things as part of your test. Simply wire the TP-Link routers WAN port to your Startlink and set its WiFi to use different fixed non-overlapping channels for the 2.4 GHz band (ch 1,6 or 11) and set a channel width of 20Mhz only.

Set the 5Ghz band to a different channel and just put the Sonos devices over to the TP-Link Subnet using ‘Update Networks’ in the Sonos App network setttings if you want to run all on WiFi (recommended), or simply wire one Sonos device to the TP link router if you prefer to use SonosNet (but remove any Starlink WiFi credentials from the App in either case).

Note: Only use SonosNet if you do not have any of the following products

• Roam/Roam SL
• Move/Move 2
• Era 100/300

With SonosNet, any wired device should be set 1metre (minimum) away from the router and use a different SonosNet channel to those in use by either router. 

Do not forget to ‘forget’ the Starlink router WiFi on your mobile controller device too, so that it does not connect to that original network whilst testing the setup on the TP-link WiFi network.

Ok, thanks Ken. I am not particularly technical but will give it a go. 
 

To confirm, router directly it the Starlink Ethernet adapter, and the switch into a LAN port on the router ? I need more ports for CCTV, heating etc 

Just for the test here, I would leave everything else just as it is - just set the TP-Link router and the Sonos devices that will connect to it, as a ‘branch’ off your existing Starlink wired network. Leave everything else in your Home to carry on using Starlink as it does now. 

So a Starlink LAN Ethernet port needs to connect to the WAN port on your TP-Link router to form a separate subnet. If there’s an ‘existing’ switch on your Starlink network just cable the TP-Link router to that and configure things as mentioned in my earlier post. You can always go onto ‘bridge’ things later, but I would keep things simple for the test here. No point changing everything at this point, let’s get the Sonos system working on the TP-Link first of all.