well actually that sub has pretty much same inputs/outpust as any other active hifi subs out there, can be connected as two channel 2.1 stereo or sub only (single sub out channel)
stereo way:
from pc use green colored plug for front speakers and connect it with your sub "from receiver" plugs, then plug your speakers with your sub ("to speakers plugs")
that will play any low frequencies on your sub and anything higher than crossover gets passed to your speakers, thats stereo 2.1
sub out way:
from PC use orange colored plug and use R channel only and connect it with your sub, use "sub in" plug there
this channel will play only when u use dolby/dts/5.1+ audio, and natively it will not play your MP3 music, because thats stereo, and to have stereo upmixed to other channels aswell, u will need mixer for it, some soundcards can do 6 channel stereo, some cant