So you have a Soundblaster X-Fi card with SPDIF-out. And a nice home theater system that you want to run your sound through. It’s okay. Everything’s going to be all right. It turns out it’s not so hard. But since this really isn’t my area of expertise, I’m going to let the kind folks over here explain everything to you. Basically, depending on what model you have, there are a few options, ranging from $180 to a couple bucks to free.
This is a problem I wouldn’t mind having — even my PC speakers (good as they are) are a bit too loud for my closest neighbor. I’ve invested in a nice pair of headphones.