Hey Egbert,
I modified the Adafruit code to work with a FEZ. The information/documentation in the code is minimal. The code here [GitHub - TwoSeven/I2CPWMDriverPCA9685: A C# class and example code for Windows 10 IoT Core or Windows Universal Apps to provide interaction with the NXP PCA9685 integrated circuit or expansion modules that use it such as the Adafruit 16-Channel 12-bit PWM/Servo Driver PCA9685 module.] is documented quite well and is the same code as in the Adafruit driver class but was written for the Raspberry Pi running Windows.
Hope this helps.