Fast PWM: Resolution in hertz
With the help of the comments, I decided to use variable PWM max values to match absolutely with the frequency. This resulted in a crispier sound that actually doesn't need the Sallen Key anymore.
For example, a low C natural, or 261.6Hz, updated 32 times for 8 full cycles of PWM give us, for a 16MHz chip, an period and amplitude of 238.
This means that having a prescaler of 8 (CS01), a period (OCR0A) AND a max potential duty cycle (ICR1) of 238, and going through 32 iterations of the sound sought for, I got the sound that I wanted and none of the wave groove that comes with a pulse duty cycle cut short.
Sure, it means less granularity when it comes to a Bb with a max duty cycle of 133, however it worked for me.