I'm loving this idea.
I have a broken NES advantage sitting in a box at my parents house. Perhaps I should do the poor mans version of this with a R-pi and liminit it to the old two button or less systems (Atari 2600, NES, Sega master system, game boy advanced, and so on). The fact that the older systems need less processing power to emulate lends its self will to the limits of the R-Pi.
Can you go in to more details on how you interfaced the Teensy USB Dev Board to the Advantage? Is there a web site you can point to with all the info some one would need readily available?