Midi Keyboard to pc speakers?

I have a midi keyboard, Casio WK-3300, that has a usb port. I have connected the usb cable from the keyboard to a usb port on my pc. I am not asking how to record or transfer files. I am asking how to have it play through my 5.1 pc speakers by usb. if it helps, my sound card is a creative xtremegamer x-fi fatal1ty pro.