After playing around with your Buzzer chip, I got a general idea of how it works now.
Lowest note (0): A0 (27.5 Hz), Highest note (255): A#7 (3729.310092 Hz), each value steps up by 1/3 of a semitone (meaning 3 = A#0, 6 = B0, 9 = C0, and so on). The buzzer sound seems to be a simple square wave too...
This gives me an idea, which may take me a while to make...