As the title indicates, I have four speakers (and a subwoofer). The system comes with two plugs. One is green, and the other is black. I am thinking that I should plug one to the output, and the other to the female slot with the 'headphone' icon next to it. It however doesn't work, and thus only two of the four speakers works at any time.

How do I remedy this? Any idea? My sound card has three outputs: speakers, something that looks like headphones, and a mic input. *has no clue*