A request to enable music output to Airplay audio enabled devices (in my case Apple Airport Expresses to amps/speakers) directly from the Plex Media Server, which removes the requirement for the Plex App to remain connected to the local network whilst playing. This will enable similar functionality to Apple’s iTunes Remote app. This is not casting from devices to Airplay, which is what the iOS Plex app currently does via the Apple Control Centre (swiping up from the bottom of the screen and selecting Airplay output).
On the Plex Apps, have “Airplay Audio” as a device under “Choose a Player”, along with a sub-list of detected Airplay devices that can be selected. This means that other media can be played locally while the server continues to play music separately via Airplay.
Sync the audio stream between the selected Airplay devices for seamless audio between zones. Continue with Airplay volume control via the Plex app when Airplay selected as player.
If users want to cast direct from their Plex apps, then they remain with “this device” selected as the player and use control centre.