There are few sound cards that have an optical out going out the back of the card. I'm assuming you're trying to run your sound to your reciever for your 5.1 you already have. You can buy sound cards that come with a 5.25" I/O insert, that would go in one of your DVD slots in the front of your computer tower. Those feature an Optical Out. Go to Creative.com and look up the X-Fi. A couple X-Fis come with them, and I know that if you get an Xtreme Music, you can buy the I/O accessory seperatly.