This was fun to figure out. I took an Atari Flashback 8 Gold and opened it in an attempt to figure out how it works, and how I could add more games to it. I was successful in this endeavor. Look at the photo gallery for help along they way if necessary. Take a usb cord and cut off the tip (not the end that connects to your usb port on pc). expose the wires, and tape or remove the red power line as its not needed, both the computer and Atari have power. The white or D - wire goes to DM on the board, Green wire, or D + goes to PM. Black or ground goes to VSS. You can see from the photos I chose to modify the case, solder the wires and leave it permanently. Alternatively one could use electrical tape for a temporary connection. with the 3 wires connected power the unit on and connect it to PC. This Atari is android powered. You can now use ADB to push and pull files to and from this unit. Once the ADB connection is established use cd /system/atgames and pull the all-games.ini file and make a copy some place safe. This file is where you add games and will need to be pushed back along with the rom files. also rom files must be .a26 format. You can simply rename a bin file to a26.
rom files go into /system/atgame/Atari, you can add a cover by pushing a png file with the same name as the a26 to the Atari folder with the rom. the file must have the same name. so for DK it would be DK.a26 and DK.a26.png. You will need the command adb shell mount -o rw,remount,rw /system to allow you to push files.
A more detailed tutorial can be found at the links below, in terms of adding and removing rom files.
My Thread on XDA:
Even more detailed forum thread:
http://atariage.com/forums/blog/687/entry-15080-modding-the-flashback-8-hd-part-two/
Tech Toy Tinker