MakerBot Industries

Between that page and: http://wiki.makerbot.com/stepstruder-mk6-with-gen3

You should be able to make it work….

I certainly have to design a new circuit (I've got no experience int that at all) for them, right?

With that in mind, I'd highly recommend you pick up a few Pololu stepper drivers. For $13 it's hard to go wrong and you can afford to keep some spares on hand.

They're painfully small and difficult to mount / heatsink properly, but Thingiverse has some carrier boards. IIRC, one is a space transformer that duplicates the MBI board size & connectors.

However, unless you have a well stocked junkbox, it might be somewhat less annoying to buy an MBI stepper driver than to cobble up something around a Pololu board.

Either choice will get your extruder running much faster & easier than trying to design a stepper driver around a bare chip.