Ran into a couple things w/ the audio browser I can figure out. Hope someone can help.
First, I couldn't drag & drop an audio file from my iTunes library into a slideshow. My iTunes library lives on a drive connected to my Airport Extreme.
2nd. As a work around, I imported 2 tracks into the slide show. This allowed me to place the music into my slideshow.
Not knowing I had been succesful importing the files the first try, I imported them twice so they show up in the browser twice. How do you delete music files from the audio browser?
Think it would help to rebuild the Aperture catalogue?
I would test if the Aperture library is making a difference, before I try that. Rebuilding takes a long time, and occasionally it can corrupt the library further, so you should not do it without a current backup.
To test if the library may be causing this, create a new, empty test library (File > Switch to library < Other/new), then import a few image files and try to access iTunes. Does it work?