That is a card or software used on Asus boards.
You should go to the Asus website and look up your board. The drivers/software will be in the download->Utility section
http://support.asus.com/ServiceHome.aspx?SLanguage=en
If you want an exact site, you will need to tell me your motherboard model and exact version of Windows
I call it software because the X-Fi SupremeFX 2 found on lets say the Maximus IV Gene-Z is just a software enhancement and the chip it self is realtek.