Import mp3 into FF6?

MP3 -> FF6 music format conversion is impossible. As PowerPanda said, there are tools like PetiteMM and TinyMM to convert a 8 channels midi to FF6 MML format, but that just gives you notes and octaves, everything else has to be added manually to the MML file. Then you convert that MML file to FF6 binary song format and insert it in the ROM with another tool like mfvitools. There's also the MSU-1 option, you could install the audio hack and define your own OST instead of using one of the mod preset. It's less work than music hacking but you still have to manually add loop points to your tracks in order for them to loop properly in the game.