[JHolland]

So explain then why only 9 timed outputs are possible on the 2560, if it's not a hardware limitation?

Because the timers that would usually be used for hardware output are instead used to create a scheduler. Its a unique and very unconventional way of doing it and when I queried this years ago the reply was a link to a tutorial with example code on how to use output compare, unfortunately it was written by someone who didn't actually know how to use output compare - it still exists:
https://www.robotshop.com/community/for ... upts/13072