If this is a 10.8.1 problem then they must have heard from many users by now.
Ever since upgrading to Mountain Lion on my MacBook Pro (late 2008 model) I've been having problems with streaming music wirelessly to my home stereo. For years I've used an Audioengine AW1 with all music sources (iTunes, Pandora, JazzRadio, etc.). I never had a problem until I upgraded last week to OS X 10.8 - and now have 10.8.1... The music plays fine through the internal speakers, but as soon as I plug in the USB audio transmitter, the player itself stops...unplugging the transmitter starts the player again. I've checked the Sound output preferences to reflect the Audioengine AW1, but to no avail. Sometimes re-booting the system will allow the Audioengine to play the music, but other times, no. Nor does it have anything to do with the browser (Firefox, Chrome, Safari). I'm at a loss - any help/suggestions will be very much appreciated.