If the subwoofer is not self powered then you would need an amp to drive it from the subwoofer out of the receiver.
If the subwoofer is self powered you may be able to get it to work with the right cable. A single RCA at the receiver end to both the stereo plus connections and minus of a stereo mini plug at the subwoofer end. Not a standard cable but could be made up.
The PC sub may not have enough output to keep up with a full surround system so watch the volume at first.