I've recently taken to using the optical audio out on my Apple TV, and connected it via Toslink directly to a standalone powered speaker. I get great audio output from it, but when I go back to my iMac, the iMac is suddenly dead silent. It doesn't have any audio to speak of because the sound output of the iMac has changed. No matter what I do, I get no sound—whether I play a song on iTunes, play a video on VLC, anything. Heck, even the system notification sounds are gone. After puzzling it out for a while, I found out that I have to go to System Prefs and reset the audio output of the iMac back to the built-in speakers before I can hear anything again. Why does it do this? I don't touch the audio out settings of my iMac. I just connected my Apple TV (which is connected to my iMac via wifi) to my speaker via a Toslink connection. Yet it does this every time. I don't really mind resetting the sound prefs every time. Nope... I do. It's damned irritating. Is it a quirk on my system? A bug? Or does it really do this? Any help would be appreciated.