TuneRelay is a nifty utility that runs on Windows PCs, it receives AirPlay audio from any AirPlay sender and relays it to multiple AirPlay receivers simultaneously while keeping the quality and synchronization unaffected.
Enable Multi-Room System-Wide AirPlay Audio from iOS (iPhone, iPad, iPod), OS X and Apple TV
Apple OSes including iOS, OS X and tvOS can stream system wide audio to only one AirPlay receiver at a time. TuneRelay overcomes this limitation by acting as an AirPlay receiver and retransmitting the stream to multiple AirPlay receivers simultaneously.
End to End Synchronization
Even though the audio stream passes through TuneRelay, the audio playing on AirPlay receivers are in sync with the sender. This makes it possible to watch a video on any iOS/OS X/Apple TV and hear audio on multiple AirPlay receivers.
TuneRelay retransmits the stream as-is without any modifications to sampling rate or compression. If the source is streaming uncompressed CD quality, all receivers receive the exact same uncompressed audio bits as sent by the source.
Remotely control volume and connection state through an iOS App.
TuneRelay requires minimal CPU resources and memory footprint making it possible to run on any system with compatible Windows version.