Happy to hear that you're up and running.
This was a particularly frustrating problem, and I've got no idea why your fix worked, but all's well...
As per joemike, the iTunes related files have been incorporated into Music Library.musiclibrary.
I've got both of my libraries in "Media" folders so if a Music update needs to address them, it can find them...but I'm not certain that it wouldn't find them anyway.
