Allegedly, on or about 18 December 2018, Rick Stevens sent:
Note that the "standard" packetizing protocols will exhibit these synchronization issues even on a LAN because you have no control over the clients' playlist request timings due to the inherent asynchronous, transaction-oriented nature of the connections.
As soon as you use playlists, you're going to have synchronisation issues. Each player wouldn't begin loading from the playlist at the same time, as the first problem to deal with.
You'd need to be broadcasting a stream, and have players that that simply replay the current live stream, to get past that hurdle. As well as for being able to handle what one speaker system does when it recovers from a signal hiccup.
The second hurdle will be decoding delays. You'd want to be using the same playback hardware and software, on every player, to *try* make everything have the same inherent delay.
WiFi speakers have special protocols to manage this kind of thing.