Running on Makerbot Gen3 motherboard

I've been trying to get GRBL running on an old set of Reprap/Makerbot Gen3 electronics that I have. Any help is greatly appreciated. Here's some notes on what I found:

The motherboard is based on sanguino with an Atmega 644p. It has an SD card slot and an ATX power supply connector on board to power the board. This is so the original 3d printer could print from the sd card without a PC attached. There's a lot of these out in the wild and they're considered obsolete for 3D printing so they can be purchased cheaply.

The stock grbl installs fine but there's no response in the console. I found daapp's fork, particularly this commit: https://github.com/daapp/grbl/commit/76a210061047837eaacf5b1033c76a4f3d3cca70 and it worked great.

Outstanding Problems: If you connect the ATX power supply, the 5V standby voltage will power the card but the PSU will NOT turn on. You can talk to GRBL from the console but no power will be supplied to the stepper drivers. To enable the ATX power supply, DIO14 needs to be set high. Not sure where or how to do this.

Pin Assignment: If I'm understanding things correctly;

• X-Step D15
• Y-Step D23
• Z-Step A4 (Is this the same as D27?)
• X-direction D18
• Y-direction D22
• z-direction A3 (Is this the same as D28?)
• X-max limit D20
• X-min limit D21
• Y-max limit A6 (Is this the same as D25?)
• Y-min limit A5 (Is this the same as D26?)
• Z-max limit A0 (Is this the same as D31?)
• Z-min limit A1 (Is this the same as D30?)

Reference: http://www.hobbytronics.co.uk/atmega644-arduino http://reprap.org/mediawiki/images/d/da/Motherboard_1.2_schematic.png http://reprap.org/mediawiki/images/1/1b/Stepper_Motor_Driver_2.3r1_schematic.png