have a look at the end of the stepper drive boards and it will state what type they are, probably a cd20 or sd 20. Page 23 of the digiplan drive manual shows the pinout for the end connector, and pins 26 and 28 of row c are the dir and clock positions. You'll need to find the wiring that feeds these signals into the drives and isolate them from the main board, then it's simply a matter of putting the buffer board between the breakout boards output and these points