This will require a bit of thinking to get 50-odd channels of input and output performing the way you want.
CPU wise, a Mega 2560 should be ok, but will still need some thought on the I/O
I’d also consider there could be a case to add a small coprocessor in each drum with a serial link - to reduce the amount of wiring and for ease of bump in/out, but this is just a side thought.
Sorry, I lived in Toronto 50 Year’s ago, but now I’m a bit far away!