Michael:
I' don't know if I understood correct your doubt, but you could make with software, many PWM outputs channells using TIMER2 16 bit autoreload mode, in only one microcontroller, ( you must NO think about only one dedicated PWM output ), you can choose the number of level's or bit's resolution from 0 to 16 bit, in each channell, it depends of your CODE SKILL's. ( turning on or off each out, depending the 16 bit counting of the timer ).

Another point that is not clear for me is: is nescesary to interface it with an I2C ?, could be an SPI interface ?
Regards.