Track 35: "Unknown 1" sounds like the tune that plays when you collect a boss crystal at the end of a world, as heard in this
video (at 5:03, 7:38, and 11:00)
Track 36: "Unknown 2 (Armor Joe Alternate 1)", so the "Armor Joe" tune is the one used in the cutscene
here (at around 13 minutes in), but Track 36 seems like the standard boss music, that plays during the intro to most bosses, as heard at 4:20, 6:25, 9:00, etc)
Track 37: "Unknown 3 (Armor Joe Alternate 2)" appears to be a continuation of the "Armor Joe" track, as it occurs immediately afterwards, at 14:03. These two cutscenes are technically separate though, since there's a fade to black in between, as seen in actual
gameplay (at around 5:30)
Track 39: "Unknown 5" should be the multiplayer victory (when you win the entire match, not just a round), as heard in this
video, at around 10:15
Track 40: "Unknown 6", isn't this Professor Ein's theme? I can hear it in this video full of
cutscenes from the game at around 2 minutes, during the intro cutscene. I don't know the actual name of the track, but it seems to play after each boss battle, when Professor Ein calls in (as heard at 5:15, 6:45, 8:02, etc)
Track 41: "Unknown 7 (Variation of Unknown 6)" appears to be from the same cutscene, when Professor Ein is explaining the Hige Hige Bandits, at around 3:30 in the video linked above.
Track 42: "Unknown 8" is the Game Over/Continue? theme (as shown in this
video)
I still haven't found Track 38: "Unknown 4" in my quick search, but I do plan on replaying the game at some point in the future, so I might keep an ear out for that track. It sounds really cool.