In-game recording of FMOD and mixing tracks

Hi, i would like to record the output of an FMOD track and be able to put more tracks on top of it (So the player can record different tracks and put together a song that he plays in-game right now).

I have read about DSPs and its logic its kind of hard to understand for me even tho i know scripting, since it has so many audio related functions.
Could you help me put together the overlapping of this recoridngs? I guess i could the given recording examples provided, but they output to MP3.

Thank you!