A bit off subject here -In my case, most of my AirPlay usage is for background music, and in particular to multiple devices and speakers in different rooms, and floors in the house. One recent use involved my WiiM Amp in one ground floor room, a RIVA Arena speaker in the ground floor hallway, another RIVA Arena on the first floor landing, and another RIVA Arena in a second floor room. All played without any issues, and as far as I could determine, they all seemed to be synchronised as I walked from room to room.
I was hoping to be able to do this sort of thing using the WiiM DLNA Casting feature, but can't do it with the current beta version.
Edit: For those not familiar with RIVA, here are the Amazon links for RIVA Arena, and RIVA Festival speakers. These are the ones that I would like to use with WiiM DLNA Casting.
Regarding Riva Arena speakers. Be aware that Riva seem to have been resurrected and are selling upgraded versions of the Arenas on Amazon US and have firmware updates available on their own website. I've updated my 2 Arenas and posted links etc on a few threads on Reddit regarding the updates.