There is a built-in amplifier inside the serial subwoofer, as I remember well with its own filters, which supports not only the subwoofer but also the rear speakers.
I see two options here:
1) Connect an additional amplifier to pins 6 and 7, where, as I remember correctly, the signal from the radio comes to the factory subwoofer (6 left, 7 right). Then both subwoofers will run.
2) Disconnect the complete serial subwoofer and connect an additional amplifier in its place. And here are two options:
a) Amplifier to drive the subwoofer itself, but then the rear speakers are lost;
b) An amplifier or two that drives both the new subwoofer and the rear speakers of the car. For the left speaker, these are pins 2 and 3, and for the right speaker, these are pins 9 and 10.
Pin 1 is a constant plus from the battery, although when adding your own amplifier / amplifiers, I would recommend tightening the thick power cord.
Pin 5 is the so-called remote signal, used to control the switching on and off of the amplifier.
I hope I did not mistake the pins in the ankle, but if necessary someone could confirm it.
