I just did a mach3 conversion of a chinese CNC router and it works so well I'm thinking of doing the same thing to a small Roland MDX machine. There's nothing wrong with the Roland but a consistant interface and the ability to use the same post-processor on both machines would be nice and I have an aftermarket 4th axis which I could run simultaneously with Mach (at the moment there's a selector switch which swaps Y for A). The hobbyCNC board looked like a perfect solution except the little tiny Roland steppers are 4-wire which aren't supported.

So any suggestions for a simple 4 wire stepper, 4 axis parallel port controller?

Xylotex - 4 wire - 4 axis. http://www.xylotex.com/4axBoard.htm

checkout gecko's new 4-drive 540, I believe individual drives are replaceable (long cheap drives thread in Gecko sub-forum)