A2D2 Stream works with Google Home speakers, and third party speakers/systems with Chromecast built in.

Simply open the A2D2 App and select the Chromecast speaker you'd like to listen on from the list of automatically discovered devices. 

Please note, due to the way the Chromecast protocol works, there's a few seconds latency. You'll know the integration has started as on Google Home speakers, you'll hear a cute 'chirp' from the speaker when A2D2 Stream starts its connection