Hah, well, I built the PCB and I couldn’t get it to work. I got frustrated and busy, and never really put a lot of troubleshooting effort into the board. Then, I bought a new house, and decided to get a Monoprice 6 zone amp. FWIW, I do love this amp as you can pipe different music to different rooms.
Sorry I can’t be more help, but if you use pre-built relays you could probably cut out much of the potential points of failure. I haven’t gotten everything set up yet in the new house, but I did have a lot of good luck with Arduinos/Particle boards and MQTT.
Let me know what you come up with!