The thing is NGFX SoundBuilder only supports one solid track. You can't add a separate loop file or anything. It just has a loop toggle. That's why I think something similar to what I posted will work best.If you are familiar with Python, you can try to run it through 'PyMusicLooper' see here:
https://github.com/arkrow/PyMusicLooper/blob/master/README.md
This program takes a 'music.wav' and it will make intro.wav, loop.wav outro.wav for you. I used it a lot for my projects![]()
If you listen to the way the Blazing Star stage 2 music loops, the timing is not quite perfect, so it stumbles slightly, but to me it's just part of the original experience.

I was so overwhelmed by the main problem that I didn't notice.