That is a bit of a rats nest!


Stepper motors are controlled in steps. For a common 2 phase stepper motor, each step is typically 1.8deg (200 steps per revolution). Each step is moved between by switching of one coil, and turning on the next (hence the four wires). (the actual stepping is a bit more involved, but I'm keeping it simple!)
If you drive a stepper motor at low speed using full steps, it basically jumps between steps, and provides rough movement aswell as limits speed due to resonance issues.
Half stepping means instead of the driver jumping between steps, it applies aproximately half power to the next coil, while still maintaining half power on the previous coil, so the motor is held approximately between steps. This improves low speed movement, but is not as good as modern microstepping drivers.

With a microstepping driver, the drive gradually transistions between full steps, by transferring power between coils in a series of microsteps. Modern drives typically use 8 microsteps per full step, as there is nothing to be gained from more steps for typical CNC applications. This leads to far smoother motion, and a bit more accuracy (due to the way microstepping works and the motor torque charachteristics the exact position may vary slightly). The smoother motion means an easier life on the machine, faster speeds, and a better finish (within the limits of the actual machine itself).


If you were handy with a multimeter, you should be able to figure out what's not working, but by the looks of it there's various bits in that control box that modern drives and break out boards don't need.
You really need to start by doing some wiring diagrams. Start at the power in, and trace the wires through the various components to the drives. Then do the same with the wires from the parallel port.

You may find buying 3 new drives, a breakout board, and starting from fresh is easier and quicker.