I've ordered a male-to-male IEEE 1284 Type C cable from here:
http://www.l-com.com/d-sub-ieee-1284-mo ... ch-36m-30m
Upon connecting the keyboard to the connector box, it booted up successfully! I was so happy to know I found the right cable and that the keyboard was functional.
If you were searching for that cable, there you go. I'll post pictures as soon as I have more time.

edit: connector box ports differ greatly from model to model. I'm specifically talking about the Model 4 (IV) connector box, which accepts a male port for keyboard communications.