Hi @Underdoi,
Welcome to the Sonos community and for letting us know about your concern. Let me help you with this.
We respect that you wanted to replace your Sonos Play 5 motherboard, but it is not recommended that you perform it on your own, it may cause potential danger to you. As our first priority is always the safety of our customers. I recommend reaching out to our phone support team for further assistance and to check out of warranty and loyalty program options to provide the best recommendations regarding this concern.
If you have any questions or run into any other issues, please do not hesitate to contact us, we’ll be glad to assist you.
I don’t have the board sizes but I’m heading the same direction putting a Raspberry Pi and small amp in my defunct Gen 1 Play 5s. Only real challenge will be how to connect the speakers and designing a crossover.
It will be safe enough as it will only be fed 5 volts from a wall charger.