So perhaps its something like this:

DESIGN (CAD) > G-CODE Conversion (CONVERTOR) > Parallel Output (CAM, ie MAch 3) > Parallel Output to Stepper Board > Output to Steppers on CNC
Perhaps: like this:

DESIGN (CAD) > G-CODE Conversion (CAM) > Output ( ie MAch3 or Linuxcnc) > Parallel Output to Stepper Board > Output to Steppers motors on CNC. ..Clive