32G is a hell of a lot of music! Even as 16 bit 44.1kHz .wav. In any case you can still convert to .wav, mix then convert back. I guess there will be some tiny loss but that would depend on the quality of the original MP3?I have a problem with wave in that my portable player is a microcontroller running the VS1053 sound chip. It only accepts micro SD cards of 32 GB or less. I can't even fit my MP3 library on 32 GB, much less wave files.
Dave.