Regarding USPS Media Mail shipping, I ship music box discs that way
occasionally and have had no problems.  You'll find it in definition
4.1 of the "Content Standard for Media Mail" if you go to the USPS
website with this link:  http://pe.usps.com/text/dmm300/173.htm 

  "Sound recordings, including incidental announcements of recordings
  and guides or scripts prepared solely for use with such recordings.
  Video recordings and player piano rolls are classified as sound
  recordings."

If you think you'll have a problem with a postal employee, simply print
it out and show it to him/her!

Nancy Fratti - Nancy Fratti Music Boxes
Canastota, New York, USA
http://www.nancyfrattimusicboxes.com/