Translating Stepper motor driver outputs (A-,A+,B-,B+) back into clk,en,step
I would use optocouplers. You will need to calculate the values of R1 and R2 to get reasonable currents.
You will need to convert the PWM signals using software.
If you can turn off the microstepping, it will be easier.



simulate this circuit &ndash; Schematic created using CircuitLab