Ok, I did. I re-soldered it to the Teensy and, this time, pushed the stripped ends of the wires directly into the appropriate holes of the ADB socket (which I can confirm works with my Griffin iMate). Still behaving the same: all three LED lights steady dim and keyboard unresponsive (and, by the way, this is happening with both of my M0115s).
Needless to say I'm confident the wiring is good (but I'm willing to play with it some more if there are no other options).
A question about compiling:
I installed Crosspack (and restarted computer/Terminal), but when I tried to execute the "make" command in Terminal the output told me I needed to install Xcode. I then installed Xcode and compiled (seemingly successfully). So what's the point of Crosspack if Xcode is what is needed (or, are they both needed)? Could it have compiled incorrectly?
Thanks.