Hrm. Well, the literal translation of the Big Nine's japanese name is the 'Nine Great Kings of Heaven', so that would make sense.

OOOH! And I'd forgotten all about Jackie and PCHammer.

I'm not sure about Mace and Neo, though. The tricky thing is, in Giant Robo, sometimes the difference between one of the big players (Big Nine, Magificent Ten) and the 'flunkies' is kinda blurry.

Hell, the only two members of the Big Nine you even get to see are Chief Chujo and Taiso. And for all that Ko-Enshaku is one of the scariest members of Big Fire, he's merely a flunky.