first, I would like to show you our Multiroom Audio Configurator which might help you with your plans as well.
If I understand, correctly, you want to setup the system in three rooms: home cinema, bathroom and kitchen.
Every Pi driven by Max2Play is capable of streaming audio to several other Pis serving as clients. One solution is to name each Pi after the room and to set up the Logitech Media Server (LMS or Squeezebox Server)on the Pi „Home Cinema“ and launch the corresponding Squeezelite Players on the „Bathroom“ and „Kitchen“ Pis. In the interface of the LMS, those players appear in the top right corner in a dropdown menu. From there, you can control the playback separately or synchronized for each room.
I am not sure at the moment how your existing hardware is connected. Do you already have speakers in your kitchen and bathroom connected to your amplifier? What I want to point out is: There is no need to put a Pi in each room if you have speakers in place receiving audio signals from your cinema amplifier. In that case, you could place two Pis in your home cinema, let’s say one „Kitchen“ Pi with the 7″ touch display running the LMS and the Squeezelite Player and one „Bathroom“ Pi with the second Squeezelite Player, each with an HiFiBerry DAC+ or an IQaudIO Pi-DAC+ connected to the RCA inputs of your amplifier. The 7″ touch display could be used to control all Squeezelite Players via Jivelite (visualization for Squeezelite Players). But again, I am not sure at this point, we might have still clear up things.
Maximilian from Max2Play