Using SPDIF cable with 42 inch vizio?

The model for my tv is E42OVA, and what I am trying to do is connect my tv to my sound bar with an SPDIF cable, the problem being sound is still coming through the tv and not the sound bar. I was under the impression that that SPDIF out slot would send allll the sound on my tv to the sound bar. I have my laptop and XBOX 360 plugged in to the tv, and would like the sound from both of them to go to the sound bar. I can get my 360's sound to go through using the component cables, but there is no SPDIF slot on my XBOX, and the laptop doesnt have anything but an HDMI slot. My sound bar has no HDMI slot, only component and SPDIF. Hope this wasn't too confusing, thanks guys. :)