I was pretty sure i'd seen reference to external stepper drivers for the Rambo board someplace. It took me a while, but i found it again, in one of Tom Sanladerer's Youtube reviews. He points out (at time 3:03) pins that can be used for external drivers in case the on-board drivers fail. You'll have to do a bit more digging, but i'm (98.7%) sure it's doable.