Ahh, well, here is a half-answer. I was actually using a 7.5 2.0A, and no, I don't think 7.5 2A is enough.
Once I used a 9V 5.0A, the serial accepted input!
The multi i/o board, however, still crashes the cpu. A friend is providing me a chip remover and I'll reseat the chips and try it again.