Build your own multi-room audio system with Bluetooth, Airplay, and Spotify using Raspberry Pis
Multiroom-Lautsprecher mit Raspberry Pi | RC-Modellbau-Portal
Allo Boss DAC 3 Complete Kit for Raspberry Pi Multi Room Audio Streaming and Accessories, Power Supply and MAX2PLAY System: Amazon.de: Electronics & Photo
Build a multi-room audio system with Raspberry Pi — The MagPi magazine