I am attempting to build a control surface for controlling audio recording software.
With the Due running at 84 MHz is it feasible to multiplex the simple on/off switches and still have a very responsive system, thereby getting within the avaiable pin count?
What is a "control surface"?
Encoders really need interrupts to avoid missing any pulses. 4 encoders will need 8 interrupt pins. No Arduino has 8 external interrupt pins. And, no they can't be multiplexed.
The Arduino Due board has powerful interrupt capabilities that allows you to attach an interrupt function on all available pins. You can directly specify the pin number in attachInterrupt().
am I missing something?