Okay here is the deal. I have had a klh reciever 5.1 and 5.1 klh speakers, center left right left rear and right rear and of course the sub. Now here is the thing I recently bought a optical cable for my brand new xbox 360, but when i put it in my reciever and 360 and set my reciever to optical 5.1 mode my rear speakers make a loud hum noise even when i put it on mute! I really dont know why i cant get sound in the back. Even the center channel doesnt do anything. the reciever shows all of the speakers on and i am very confused. Am I hurting anything. I really want the best sound and I read the manuals and still cant figure it out. I suck at my reciever and know Nothing about opitcal cable stuff. please help me !!!!!