heckboy

I have recently purchased the Promedia 5.1 speakers and am having some problems getting them to work properly. I am running them from my Powermac G4 (latest OS X), which is connected to my Sonica Theater via USB which is in turn connected to the Klipsch control box with a Digital Coax cable (Monster Cable). The M-Sonica Theater control panel clearly shows all 5 audio channels active to varying degrees when I play a movie, but it is only the left and right audio channels that are being fed through the 5 speakers. I know this because when I mute the front left and right channels in the M-Sonica control panel, all of the speakers go dead. Somehow, the separate channels are not being received and split properly. Is it possible that the input port on the Klipsch control box is bad? The input button on the control box is selected to DIGITAL COAX. My digital coax cable can't be bad, could it? Please advise. Maybe I am missing something.