Sound card:
http://www.newegg.com/Product/Produc...82E16829102040
Best $90 I've ever spent on a purchase meant specifically for gaming.
However, the only real way you can take advantage of a sound card like that is if you have an optical-in headphone. If you're looking for a USB or normal 3.5 mm jack, well... what's wrong with on-board sound?