I attached USB speakers to my Mac before I booted the system this morning (I always shut down when not in use) - they showed up on the Sound option in System Preferences - with speaker control adjustment loud soft - so I double clicked them - closed the window -brought up ITUNES -NO SOUND - opened system preferences SOund and double clicked on Internal speakers and sound came up.
Was hoping - because they never showed before on this system the USB speakers would work - no such luck. (these are those pretty Apple crystal ball speakers that apple decided not to support at some point with newer systems - as they showed up hopped they would be supported. From Within Itunes posted the problem to ITUNES feedback.
In order to get the sound to the internal system - I did have to double click - not just highlight.
(am on snow leopard)