Connecting plex to whole house audio system.

Hello folks,
I am building a house and plan on installing HTD’s Whole House Multi-Room audio.
The central hub takes input from sources and controls the 6 zones.
I have plex media server running on a MAC and currently streaming to Apple TV
Question:
What would be the best way to stream to the HTD hub?

thanks in advance

If your house system cares about distribution and zone management, you’ll only need an audio source, right?
Use a ‘Chromecast Audio’
https://www.google.com/intl/en_US/chromecast/audio/

You can use (almost) every smart phone, tablet or PC on the house to switch music.
https://support.plex.tv/hc/en-us/sections/200276908-Plex-Companion

I might suggest getting a Raspberry Pi and setting up another Plex server just for music.
Install a VNC client on it also and run it headless. Mine is mounted on one of my monitor arms, tucked out of the way, hardwired to one of my switches.
You can use the Pi to be the audio source if you mount it close to the HTD or use Chromecasts like @OttoKerner suggests.
I use Chromecasts and having a separate Plex server for my music allows me to have a dedicated device that just accesses the music so anyone can can use it without messing with our movies/TV shows.