Hack the USEN terminal to play Bluetooth music from the built-in speakers

Hello, I'm incompetent.

Introduction

My residence comes with a built-in USEN system.
However, since I don't have a USEN contract, I can't use it, and it's just become junk.
I confirmed that there are speakers installed at the top of my residence, and if they can produce sound, I imagined that I could easily connect them to a digital amplifier and play music, provided I could find the audio cables.

Disassembly

First, I'll try disassembling the USEN unit itself.

It seems this is where the AC power is supplied and the speaker cables are connected.


Since I don't have an electrician's license, I shouldn't touch the 100V wiring in the power supply section.
However, the power around audio systems is typically 12V/9V even within a digital amplifier, and the voltage in the speaker world, which is below that layer, is even lower, so it can be handled.

Connection

So, I'll connect a digital amplifier and try to get some sound.

It was easier than I thought.

Conclusion

It seems that USEN terminals commonly use BOSE speakers for their built-in systems, so the sound quality is quite good.
The title is grand, but all I really did was wire a cable to the speakers.