Current limiting on a stepper controlled by L293D on an arduino board
Look at this Digital Potentiometer on Arduino's Website

On this one you have 64 setting of resistance.

Connect these like you would resistors. It's basicly 64 resistors that you can "switch" the resistor via your Arduino sketch.



You'll need to find a different chip for the right resistance levels and wattage. I didn't look at this one hard but it was only controlling a LED: not 1.6 amps. It might, but I doubt it.

And it would take only 2 pins for both motors, even if you need four chips because they use the same protocol than allows multiple devices on the same 2 lines.