Well, I might have got it all sorted. As it was configured when I posted this thread, the only thing hard wired was the Boost. And as mentioned, it did nothing to solve issues but I left it in the system anyway.
So I decided to go ahead and wire several of the other components including the Amp and the speaker on the back porch.
As soon as I plugged anything other than the Boost into the router the wi-fi went down everywhere. Unplug and everything is fine. I can't tell you how many times I restarted that router with every combination imaginable. Finally I unplugged the Boost from the router. When I did I could plug in the Amp and two other speakers in the house and everything works and seems to be working well for the first time in ages including the porch speaker which is the furthest from the router.
The irony is that the $100 plastic box not only didn't help solve the problem it actually made things worse.
Still frustrated with Sonos. The implementation of its network is really pathetic but if it continues to work okay I'll keep it for now.
I live in dread of the next 'update'.