Hey there! I know that Aluigi made a script for Magnetis since I extracted the archive on Steam/PC and it was also a .nac file.
You'll need QuickBMS, along with this script: https://aluigi.altervista.org/bms/magnetis.bms
All of the music is in .OGG format and is found in the extracted data/music folder, but none of it loops.
The looping data for the tracks will be in one of the .nut data files. I forget which one. You can open those in any notepad/text editor.
EDIT: Okay, found the looping data for you. It's in gameParams.nut.
Like for the music for Solo mode, you'll see this bit: "bgm_solo_repeat <- 57932".
This means the loop begins right at 57.932 seconds.
YOU ARE WELCOME.