I think my comments above a year ago, is a bit out of date and incorrect, amazing what you can learn in a year.
I am in the process of building a midi controller, 37 pots, 40 mom buttons, led's will be added at a later date.
After all my investigations and tests, I will be using 10 x 4051 analog mux ic's. I will be using an arduino to create the midi, the 10 ic's will take up, 3 x digital outs, 5 digital ins, and 5 analog ins. Same can be done on the axo.
The difference is, I can take code from others to implement, not sure if any Axo members have any code to offer for this. But if required, it should not be too difficult to implement, just need to sequence through 8 inputs on the mux through the digital outs, and read the inputs for each of the inputs 8 times for each sequence.
There are some mux's that will take 16 inputs, but I have chosen the 8. In fact now that I think about it, you may not need to code at all, all should be possible through standard Axo objects.