PS2 boards will not lose there address if the battery dies while sitting on the shelf. They will not retain the address you assign to it if the battery (or BCR) dies during the shutdown process and does not fully complete. I take batteries out of PS2 engines all the time and they never loose their address as it not stored in volatile memory. Think about it, a BCR is pretty much dead after 24 hours and those engines don't lose their address.
Most likely your 5 volt board is toast. The faulty speaker would be a good reason as to why & how but not necessarily the definitive answer.
It is a good candidate for a PS32 replacement board. When 5 volt boards start acting up, it's usually not long before they really go.
