I dusted off a license file for Mach3 I purchased and never used some time ago and got work. Breaking out one end of DB25 printer cable and attaching it to the stepper controllers for each axis was a simple and quick task. Then configuring the axis and motor profiles in Mach3 was even simpler. It was nice to make a small change and it not requiring to recompile and flash the old RepRap controller. Two hours and the whole process was complete.
The extruder controller was hard coded to maintain the extruder's hot end temperature since Mach3 doesn't have any means of communicating with the controller... yet. For now, the plan is to use a dry contact driven by Mach3 to switch power to the controller.
Running all the axis through the manual pulse generator, a successful integration was confirmed.