Summary Overall, all you need to do to hack in an auxiliary audio input, whether Bluetooth or otherwise, is to get your signal to the amplifier in the place of any other.

DIY ESP32 Based Audio Player Subwoofer Amplifier Circuit using IC TDA2030 Wireless Hi-Fi Bluetooth Amplifier Module Wireless HI-FI module is a Class AB / Class D switching function, 5.3W output power ...

There are plenty of ways to get music from your phone to a pair of speakers. You might use an aux cable, plugged into the RCA ports on the back. Perhaps your device has Bluetooth built-in ...