Disabling Speakers Enable Subwoofer??

Can't tell for sure from the wiring diagram but can you not just unplug the other speakers?
 


I tried plugging in subwoofer without the Master PC Speaker, which controls on&off/volume/bass. The subwoofer doesn't work plugged in only by itself.

I tried placing headphones in master speaker, which silences the speakers and plays through headphones, but subwoofer is also silenced. Maybe there's a software/equalizer something like that.