while flipping through my comic book #11 just the other day, i was struck by a sudden thought. when lewa nuva goes underground and sees the exo-armor being fried, he reacts by saying with surprise, "its the exo-toa!! but theres no one inside them!" now shouldnt it be expected that theyre empty, since they left them down there? lets flip the page...we see a kohrak-kal destroying one of the exo-toa, and saying, "although empty, these suits of armor still oppose us..." now how can an empty suit of armor oppose the kal? he may be simply referring to the fact that the toa can use the armor against them, but i have a different theory. i remember reading at bionicle.com that there are rumors that the exo-toa could operate independantly, without a toa. perhaps the exo-toa were trying to stop the kal, so the kal destroyed them. that would also explain why lewa is so surprised; maybe he saw the exo-toa fighting.
(if this was the idea in the first place, and im merely stating the obvious, shoot me.)