It looks like your EL Panel will work well for your needs since it is low profile and sound can be converted to light.
As you mentioned, having it wired to the speaker would be better, but not having electronics skills might be an issue.
You would have to open up the sound/light device and tap in to the input of the internal amp.
Not knowing the microphone circuit, it would be a challenge to find the best part of the circuit to wire in to.
Also, you will need the "multi-sound file control device" (MP3 player) and tap into it's earphone output and connect that
to the microphone to amp circuit. The earphone output would be a less overpowering signal for the sound/light device.
If you connect directly to the ''speaker output'' of an MP3 player you run the danger of over powering the input to the sound/light driver.
If you are going to use one power supply for both of the devices, they must be common to each other (grounded).
That way the signal from the MP3 player to the S/L device has a proper path.....
I think since you will have two separate items and they both have a volume controls, that would be easier to work with for you.
Just place the S/L driver microphone close to the speaker of the MP3 player.
Just playing with my new toy:
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