I’ve been battling with my iMac sound cutting out at weird times. I could have iTunes playing something perfectly normally, and then my computer’s built-in speakers just stop playing. My iSub continues playing just fine in the meantime.
It gets weirder when I open the Sound control panel and tinker with the settings. I can get the main sound back for a while, but it’ll eventually cut out again. Just freaky.
BTW, did you ever notice that Apple likes to append a lower-case “i” to the products they sell? For example, iPod, iBook, iWork, etc. You’d almost think that was intentional or something. 😉