I just purchased a duet set of Bose Companion II Speakers for my Mac. I hooked up everything according to the Owner's Guide yet I get no sound from the new speakers. The sound is still coming from the built-in speakers. Yes, they are connected to a power source. Yes, the volume on the speakers is turned up. It is a Mac desktop running OS Tiger 10.4.11. Obviously, I'm missing something. Any help is greatly appreciated.