I've had my Mac Mini for just over a month now and can't seem to figure out how to fix this problem. I have my 2.1 Altec Lansing speakers plugged into the headphone jack on the back of the Mini. I also have a Logitech USB headset. Most audio plays back fine through my speakers but a few things only play through the headphones of the headset. So far I've found the problem when using Windows Media Player and in all browsers (I've tried Firefox, Camino, and Safari) when Flash plays any sort of sound.