Interesting, the phone or tablet running the Amazon Music app doesn’t need to be on my home WiFi to connect to my Sonos or Echo devices. It’s being done in the cloud, almost certainly utilizing the Alexa services infrastructure. Unlike Chromecast, it never loses sync when switching focus to and from the Amazon Music app. Uses 1/3 the bandwidth of AirPlay, without the battery drain. As effective as Alexa voice control, with the advantages and disadvantages of each complementing the other. Nicely done, Amazon!
Now if Amazon would just fill the holes in their catalog. AutoRip helps with that, but why so many gaps compared to even Tidal?