I have a Mb C2D and a Denon 3806. I purchased a long run of optical cable (75' for my theater install). I also bought the little clip on connector that converts optical cable to the headphone jack. When I plug it in, the internal speakers turn off but no sound comes out the other end. I do have the correct optical input set to the channel its assigned to. I checked that quite a few times, and attempted to switch it just in case I was wrong, none of the other optical ports work either when set in the On Screen Display. When I go to system set up, and then audio, when the cable is out it allows me to set the volume and mute as normal. With the cable in it recognizes that there is a digital audio connection set and since there is no volume settings allowed that gets greyed out. My thoughts: Set up error. Possible but I dont think so. 75' is too far a run for the macbook to drive. Doesnt seem likely. The cable is cracked. Slight possibility. I have the wrong connector (Monoprice is usually pretty on it with this stuff tho) User error. Highly likely Ideas?