I know that your system supports Windows and Mac OS X, but can LinuxCNC on a dedicated Mac Mini be used to control the Shapeoko machine ? I do not own nor have a Shapeoko machine, but I am in the market for one.
We use GRBL for a controller so you can use any of the open controller, like Universal Gcode Sender, that are available on all platforms.
We also have an unsupported build of Carbide Motion for Ubuntu 14.04
LinuxCNC, derived from EMC2, would not work without new electronics since we do have GRBL in the middle, and that’s not part of LinuxCNC.