It doesn't appear that Colin offers the RAMBO boards anymore with his kits and instead offers RUMBA which does allow the stepper drives to be swapped out.
VIA the FAQ @ http://www.makerfarm.com/index.php/f...ked-questions/

RUMBA:
Support for 3 Extruders
Controls the temperature of the Heated Bed (needed for printing with PLA, also works with ABS)
Removeable Stepper Drivers
Support for SD Card (Needs Kliment's SD RAMPS)
Support for LCD interface (Print without connected to a PC)
1/16 Microstepping
5 Thermistors
2 fans