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.
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.
A thermoelectric generator with a radioactive source would get pretty close.
You can pretty much seal up everything else (encased in a solid glass cube, e.g.). You may want an inert out-gassing source internally, but that would probably only last a few millennia.
Choosing a trade-off between half-life and radioactive mass would be a fun engineering task. Plutonium-238 has a half-life of 87.7 years and would be long depleted before 55 million years are up. Longer term isotopes would need a ton of mass to get you there.
Funny. Contrary to everyone else worrying about the speakers and the PV's, I was thinking about the batteries failing fastest (assuming the thing keeps them to play at night).
Lead-acids would be garbage after 5 years, unless they were way oversized. After about 20 years, failure would be inevitable.
Ultracapacitors would probably last north of 50 years.
Whatever you encase the PV within needs to allow sunlight through. Diamond would probably not work for this. Silicon itself is freakin' hard (about 9 on the Mohs scale) so it would outperform even quartz in terms of abrasion resistance, and you could put its contacts on the back to keep them from eroding away. Silicon needs a different layer on the front to couple its high index of refraction to the incident light, and I'm not aware of any superior optically clear materials that could accomplish this.
Am not a speaker expert, but I'd be surprised if they didn't fail before the rest of the system. Apple's iPhone speakers will warble themselves dry after they're immersed in water, so I'm wondering if constant Toto will keep the sand out of the speakers.
An ultrasonic-interference sound generator based on piezoelectric elements might outperform a conventional speaker setup. Tinny > Short-lived.
There isn't a hope. The MP3 player itself, with solar panels, encased in glass? It could last a good long while... if it weren't that it'd be buried by sand very soon.
The mechanical transducers in the loudspeakers are the big weak point though. Suspensions, foam mountings, the voice coil magnets themselves, the cone; all subject to stress. Under ideal conditions, hundreds of thousands of hours of use. A desert is far from ideal - fine dust and temperature extremes - though far from disastrous too (a damp salty cave by a tropical ocean). Hundreds of thousands of hours gets you a decade and a half of play. So only 54,999,985 years to engineer for.
Alternative speaker tech (piezo speakers maybe?) could last longer. But it's limited! Fine moving parts are anathema to this kind of longevity experiment.
EDIT: Actually I'd encase the electronics in a giant diamond; glass would get scoured rough by the sand pretty quickly, to the detriment of the PVs.
But why not go nuclear? Not a full on nuclear reactor but one of those nuclear RTG batteries. The half life might be low but could you not keep doubling the amount until you reach the requisite years? Basically take the amount of Pu you need to power the device, and double it 20 times (half life of Pu-238 (87 years) * 2 ^ 20 >= 55 million years). This way the entire unit is self contained and you can encase it in whatever super durable material you can think of -- artificial diamond/sapphire.
Solid metal LP record with the song cast into it attached to some kind of manually wound record player (why play it if no one is there). Electronics will fail quickly in that environment, but something like that would last for a while.
Somewhat serious answer. The 10,000 year clock by the longnow foundation is going to play music with chimes, I'm sure they could play the melody from Africa if we wanted them to ;)
They are finally starting to build the thing, pretty exciting for someone one who has followed the project for 10+ years:
10,000 years might be the 1st baby step to building something to last 55 million, but that number is so large I would say it is effectively impossible.
I don't know if it'd be possible. Wind and sand is a wicked combination and it'd be sandblasted away pretty quickly no matter what. And if it didn't have the chance to float, it will be buried by the shifting sands. At that point it would probably last a while, but it certainly won't be playing Africa anymore.
Can we even build something playing sound for 55 millions years ? I mean, even forgetting the required energy, the sand, the wind, the temperature variation and the light... Just creating a music player that last so long would be an amazing challenge. I don't think exposed rocks last that long, and they do nothing.
As tudorw alludes to, social engineering: The only way to do that would be to convince people - on the assumption that their society could last 55 million years - to look after it and ensure that some kind of Ship of Theseus style Toto Gig just by having been replaced everytime it breaks.
This sounds like a good basis for a sci-fi short story about a religion that centers around a device that continually plays the sounds of their gods. They have been maintaining it for millions of years, even though they can't understand what the message is anymore...
Is there a storage medium that would last even a thousand years? The song must be stored somewhere to be played. Any sort of storage that won't be subject to bit rot at this timescale would be prohibitively large.
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.