I posted a new build of the DashClock Music Extension (1.7.0) that adds support for Amazon MP3. If you install the update and are currently listening to a song in amazon mp3, you must change tracks before it will properly show up.
I also wanted to officially announce the beta of my Music Extension for Floating Notifications. It will display the playing track and artist along with music controls. There is also a pro upgrade you can purchase which will show album art instead of the play icon (this works for most players but just in case I provided a way to test to see if your album art shows up before purchasing the upgrade). Please note you must download the beta of Floating Notifications as well.
How to join:
1) Join this G+ community: https://plus.google.com/u/0/communities/112403670127085453786
2) Join the beta: https://play.google.com/apps/testing/gonemad.fnmusicextension