To use an external driver, all you need is to do this in the configuration:
#define AXIS1_DRIVER_MODEL GENERIC
#define AXIS1_DRIVER_MICROSTEPS OFF
The microstepping will be in the driver itself, and the calculated steps
per degree should be set in Config.h accordingly.
Then you get a piece of perfboard, with 10 pins on each side, and wire
only the STEP and DIR pin, using screw terminals if you so wish.
These pins go to the driver's PUL and DIR pins.