QUOTE(Todd Watson @ July 2 2008, 11:46 AM)

It fades for the length of the last transition going into the last image, so to fade out longer, make the last transition longer.
That works. But if you want a more custom fade that is not related to the image fade, and you're on a mac, you can bring the mp3 into garage band and fade it exactly to your specifications using the volume adjust settings, then reimport your new mp3 into iTunes and replace the old music file with the new one.