Who knows how the subwoofer of the speaker is wired? My subwoofer has only 12 inch bass.

It depends on whether the amplifier has bass power output. If there is a special subwoofer horn terminal, it can be directly connected to the terminal. But if the subwoofer doesn't work without a special horn terminal, it needs to be equipped with a power amplifier circuit, which is better.

If your subwoofer is active and has its own power amplifier circuit, you can mix the output signals of the left and right channels and input them into the power amplifier.