I run my X-Box through a four way splitter(Radio Shack), along with my DVD, Satellite, and PS. You run an S-video from each into it's own port on the splitter as well as RCA's for sound. Then I run the S-video straight to the TV. The RCA's come out of the box, then I use "Y" splitters to run them to the TV and receiver. This way I can listen with the TV or stereo, or both if you want.
I know some people have different ways, and probably easier ways of setting up, but this has worked for me so I'm sticking to it!