Since he has the "USB" headphones, you do not connect it to the sound card, it connects to a normal USB port. There are no plugs to use on a normal sound card.
If you bought the headphones local, you might want to try a different pair, or there may be a setting for "boost" or something like that in the software/Windows. I can't recall what my friend did for his USB set, but he likes them. It allows a separate audio source so that he can use it for gaming.. voice comes through the headset, and game audio (effects, music etc) comes through his sound card/speaker setup.