Sounds like they’ve already been factory reset, if they’re asking for a temporary WiFi setting. Easier to connect one of them directly to your router with an Ethernet cable temporarily. Get them both set up, then change the network settings to recognize your WiFi, and remove that Ethernet cable and move them where you want. 

I did eventually work out that I needed to set up as a new system,  and it looks like there has been a factory reset ( not sure how). I've got one working on an ethernet cable plugged into my router.  How do I now change the network settings. I'm keeping the ethernet attached until I can resolve this 

Me either!!! And now I would have to buy an entirely new system cause the old is not compatible with the new? INSNAE…not happy

I don’t think it matters if you’re running S1 or S2, but you would go to (pauses while he looks at his S2 controller) Settings > System > Network > Manage Networks. 

Of course, your WiFi signal needs to match up with the Sonos Network Requirements .

I generally suggest not using 5Ghz channels, merely as the Sonos doesn’t need it to stream music, it interferes with the soundbar’s connecting with satellite device, and it is not as good for distance / absorption capabilities. But it isn’t a strict rule, lots of folks, I suspect, use a 5Ghz channel without issue.  I’m just a fan of uncluttered access. My Sonos sticks to 2.4Ghz where it can, many of my other non-Sonos devices connect to a differently named 5Ghz channel. My router has no challenges in passing data between the two.