The stepper circuits are, I believe, on the interface card. In fact, the best option you have would probably be to interface to the card, and not directly to the drive itself. Of course, you'd need to do more than just wire up a cable, you'd need special hardware, and probably plenty of software too.
Of course, all of the documentation you could ever want or need is available to explain exactly how all this works, so making a device which can read and write to this drive is certainly possible.