[ajuc]

Make a sphere from glass that is hard to scratch. Put everything inside, including the solar panels and the speakers (make the speakers touch the sphere surface so you can hear it from outside).

Sphere should be mosty empty so that it has lower density than sand - it will float on it no matter how the dunes change.

Add small electric engines that rotate against the sphere in 2 axis, that will move the sphere back to its desired geographic position slowly.

[sametmax]

The mp3 player itselft won't last 55 milions years. It will break way before. And be buried in the sand by the first sand storm, no matter how flotty the sphere is. Footballs get buried in the desert, no matter how light they are. Source: I lived in Bamako.

[ajuc]

I think if it moved a little every so often it would get unburied. But I don't live near a desert so maybe I'm wrong.

[sametmax]

You will have so many sand storms in 55 millions of years. And one is enough.