Best answer by AjTrek1
Ha! Ha! Just what I was going to suggest (sort of) :8. See below.
The only other step I can think of is "isolation". This will still require that you some how get a cable to the Playbar. Excepting the Playbar and Sub unplug your other Sonos to isolate them and preserve the new Wi-Fi credentials. Run the steps in the links to get the Playbar and Sub on the new Wi-Fi. Then plug in your other Sonos which will have retained the new credentials.