After following the instructions on the forum link provided, I have these additional notes for those that might run into this issue too:

Notes regarding the Beaglebone Black Rev C:

• The Beaglebone Black is the same board used on the bitmain antminer S2, but it has alot of extra functions since I guess it was made for consumers.

• I imaged the onboard memory with the Ubuntu image using these instructions: http://shrkey.com/setting-up-beaglebone-black-to-boot-off-the-microsd-card/ -- now it boots into ubuntu once u plug it in without an SD card.

• Supposedly the Ubuntu image auto boots to the SD card if its inserted, but thats not the case from my tests. It still boots from the onboard even with the ubuntu image installed. It will boot from the internal memory once plugged in.

• You need to image the original antminer s2 image onto an SD card. File is here: https://dl.dropboxusercontent.com/u/16075357/bitmain.img.zip (ver. 20140410 - 72MB file - hopefully its not taken down by the time u read this. Msg me if it is.) -- after the sd card is imaged you can goto the "upgrade firmware" page and load up the newest firmware from bitmain (currently 10/29/2014)

• The Boot button is actually on the bottom of the board, i kept thinking it was to the left of the reset button. In order to boot from the SD card you need to UNPLUG/POWER OFF the board then hold down the BOOT button and power it back on and wait for the 2 lights then let go.

Note: When it boots from the SD card, you can tell by seeing the first 2 LEDs light up from the right. If it boots from the internal memory, the middle 2 LEDs light up!

• I also soldered the Boot button 4 point contacts on the switch to auto boot it from the SD since it thinks the button is constantly pressed.

• Seems not to boot if I don't used a class 10 64gb SD card. I tried a really old 1gb card and it didnt boot. Also tried a 2gb and that worked.

Note: Once working, what you should see is the following while you have the cover open: ALL cards should have a "constantly" green light blinking and a BLUE light on the beagleboard card.

So spent 2 days trying to figure this out after receiving my beagleboard black from amazon. Previous to that I spent like maybe a day trying to diagnose the issue without really googlging it until I found the forum post about just buying a consumer level beagleboard for the antminer s2. Overall it was a frustrating experience to figure this out since I had to go through 5 different SD cards I had laying around to see how to image, boot, modify, and hack my way through. First things first is try to get the antminer gui screen to pop up on the browser first without connecting to the s2. then once that works, upgrade the firmware, and then attach it to the s2. One major thing is MAKE SURE THERE IS A BLUE LIGHT on the board. This indicates that the board is running and make sure you can ping the IP address at all times to see if its alive.

Quick Summary of what I did:

1. Image a new microSD with the original bitmain image (20140410)
2. Configure settings while NOT connected to S2. (I had to set my IP to 192.168.2.99 since my router was on that subnet)
3. Upgrade firmware of the bitmain image (latest 20141029)
4. Connect to S2.
5. Done!