I recently purchased an iMac and i've been trying to hook up the speakers. I have creature II speakers and I read the directions and hooked all the cables in the right spot. I plugged the main cable into the headphone outlet. The LED lights on the left and right speakers are not on, while the LED light on the sub-woofer is on. Does anyone have any suggestions for me? I can hear slight sound coming from the sub-woofer.