I don't know how they did it man.
I mean, sure, it might be the nostalgia speaking really loud, but damn, every single track is absolutely genius and it fits the pacing of the levels like a glove. A really underrated piece of art this is.
I mean... I'd say it's impossible for boss musics to be better than this: https://youtu.be/rsBdWntikDg?t=25m38s