You CAN put MP3s into the game, but it will slow down the loading process, I have found a way around that, tho.
You can make a separate download for the MP3 soundtrack.
A player can download it and put it into the game folder.
the coder makes a action to replace the MIDIs with their corresponding MP3s and it will play the MP3s without slowing down the loading.
If you DON’T download the MP3s, the game will play the MIDI music as it can’t find the MP3s to replace them with.
BOOMSHAKALAKA!