The control box came as part of a CNC retrofit kit. For those who don't know, the electronics described above use cheap components and a very simple design. In my opinion, it gets a score of 2 out of 5 in terms of sophistication and robustness. If could do it over again, I would have bought a better CNC retrofit from a different company like below. 

When buying a retrofit, you want to look for bipolar stepper motors instead of unipolar stepper motors. Bipolar motors are faster and give you better torque at high speeds. The control electronics are more complicated but it's worth the additional cost. You'll realize the extra speed is important when it takes 30 minutes to make a simple part just because your unipolar stepper motors are too slow. Also, you want to buy a control box with some type of smart controller that handles the stepper motor timing. This will allow better control under a non-realtime operating system like Windows. I would recommend the CNC retrofit control system from Flashcut CNC.

I plan on doing a quick modification to this design by adding a 4th axis control and a microcontroller for handling the stepper motor timing. Details will be provided soon.