Out of inputs

I have a 7i92m, 7i77, and a 7i72. All 32 inputs are in use and i need 3 more digital inputs. The smart serial rs422 port on the 7i77 is used by the 7i72. What is the best way to achieve this?

IDC26 connector on 7i92 has 17 more IO, but those are very sensitive so care must be taken for wiring and signal shaping.
Using voltage dividers (simple 2 resistor thingy) you can use those for anything you need.
Or get a cheap BOB and IDC26-DB25 connector, but that limits to only 5 inputs.

The 2nd port on the 7i92 can be used.
A opto isolator board, something found on eBay or AliExpress or a dozen places, can be used to provide voltage translation.

Is there a mesa option to achieve this? Would it be possible to use a spare encoder input on the 7i77?

1 of the 3 inputs needed will be used for a prox sensor to home ATC turret.

Yes, you can use spare encoder pins as general purpose inputs.
They will work with 5V signals if set to single ended mode.

The encoder inputs have a 2K pullup resistor to 5V (so will work
with NPN proximity switches) The single ended encoder inputs
are safe to +12 and -7V.

The pin names will be:

hm2_7i92.0.encoder.0x.input-a
hm2_7i92.0.encoder.0x.input-b
hm2_7i92.0.encoder.0x.input-index

That's perfect. Thanks for the help.