No sound through HDTV setting?

Well here is the deal. I have the component HD AV cable for me Xbox 360. Anyways I have the Blue green and yellow grouping plugged into the yPbPr jacks (which say component in on the tv) and the red and white plugs (thats grouped with the yellow plug) into the AV in jacks. Now if I set the cables TV and then switch the tv to video, I get subpar looks but audio. If I then switch to the HDTV setting on the cables and go under the yPbPr input on the tv, i get amazing resolution quality but no sound at all. What is the deal? Oh by the way just incase me TV sadly does not have any HDMI support. Any help would be greatly appreciated. I am tired of playing Dead Rising with unreadable text haha.