Sorry it took me so long to chime in here. Did not have much time for the forums lately.
Here is my take on the situation: there is a way to make your own driver out of a whole bunch of MOSFET transistors (need two per an end of a bipolar stepper, and it has four ends, so 8 transistors), a heap of MOSFET drivers (IC that makes TTL control of a MOSFET easier) and a heatsink(s). So, it's a pretty involved device. And the issue of microstepping as well as current sensing and feedback would still have to be solved. You can use an Arduino as a stepper driver, but it will run out of available I/Os really quickly. With all proper feedback, you might not even get to control two steppers with one Arduino.
So, that's where the proper dedicated driver becomes so important. I would have to admit, for a powerful motor I would much prefer using a specialized IC rather than trying to use an Arduino as a driver, although this sounds like a fun project. Trying to bootstrap the Allegro chip used in Easy Driver to a too powerful a motor won't probably do much good. I cannot say I know much about more powerful chips, sorry.
But as far as trying to get SOME rotation out of a freewheeling stepper, even a powerful one, using an Easy Driver, I think you should be able to use that schematic with the code at this site that you referred to without any modification with one caveat: the code here was written for the Allegro A3967 chip, whereas BED board has the newer Allegro A4988. I have not tried that one yet.
If you have ENABLE connected as per the schematics, try to disconnect it (it will make it always enabled and lead to excessive heating), and see if your motors at least twitches. The code assumes that each button press results in 160 microsteps (or 20 full steps if in 1/8th mode), so it should result in something like 18° angular movement of the rotor. You cannot mis-wire the motor itself (it can only be wired to rotate in a wrong direction, easy to correct later), so don't worry about the motor, double-check the other important connections - Step and Direction
Anyhow, see if you can post more details, a picture perhaps, of your setup, I will try to be more helpful.