In star control 2, if you have two players in a supermelee, each will be using five keys for their ships, which could in theory result in as many as eight keys at a time (since both right and left simultaneously is unlikely).
Also, slightly more relevantly, if you play Dark Souls via Steam without a usb game pad, you'll be using the keyboard in all likelihood since it's decent and the mouse implementation is reportedly terrible. This could easily result in more than 6KRO if you're strafing, camera-looking, and attacking/kicking/dodging/iteming/whatever-else-ing at the same time.