My uncle has just purchased a new 24" a week ago. He orderd JBL creature II speakers because he liked mine so much. He got the speakers, and plugged them up and attached them to the headphone jack on the back of his iMac... and he gets no sound. He tried even a pair of headphones and got no sound. The sound was playing fine out of the built in speakers. As soon as he hooks something to the headphone jack, the built in sound stops (as it should) Anyone have any idea if the jack could somehow be muted itself or other things I could check. My only mac is my Powerbook G4 1.5ghz and I have plugged this machine to speakers 100 times using my headphone jack, and never had to change any settings at all. Thanks!