I just realized while browsing the forums they added a new piece to the game, called Boss2. It was playing during the finale of C42, but I never actually heard the song, as it was too quiet during the boss fight and tended to be drowned out by the fighting. And yes, all of the sound bars were at max and my own sound was quite high as well.
I'm listening to the other tracks as well, and I noticed they were all much louder than Boss2. Something tells me this wasn't on purpose.
Actually, the same goes for the new slime theme -although it can still be heard. It's just I noticed all the tracks were slightly louder than the slime theme.