Its amazing to learn from your experiences, so if I got you right you have a pc with parallel port and that goes to a grbl controller then a breakout board and then the drivers and the steppers. And you use custom software without going into the hassles of CAM.
What breakout board did you choose to go in for or did you choose to go in for? Also modern PC's dont have a parallel port so do you have a PCI card that you have inserted in you PC? Also are you running on linux or Windows?
Its fascinating that you could get a CNC up and running in as low of USD100.