If it is the boss rush mode, I remember doing that without any big problems. I found it MUCH harder to beat the scores needed for those special attack minigames.
I agree. You need to do extensive grinding (Lowest level I beat it at was 41, which is high for the game), but it becomes rather easy if you can dodge attacks and do the Special Moves correctly. The Cholesteroad and Broque Madame... are unfair. Just INCREDIBLY hard.