It works! I had a buddy of mine give me a hand and help diagnose the problem. For those that are curious, there are 2 wires on the main board for power. One red and the other brown. There is also a black wire for a chassis ground. The red wire is negative, which connects to the black wire and to the outer ring of the adapter plug. The brown wire is positive (go figure) and is soldered to the center tip of the plug.
When we did this (after testing) it seemed nothing was happening. So, I hooked up the A/V cables and lo and behold, Keith Courage pops up!! Now, I have yet to check the operation of the cdrom drive, I'll do that later. For now I have to get a 5.5mm x 2.1mm plug and install into my Duo. I also have to make an adapter cable to use my TG-16 controller with the Duo, easy enough.
Oh yea, the only thing that saved my Duo from getting damaged by wiring the power backwards was a nice diode, placed inline right after the fuse. Thanks NEC!