Like Jim says, Crowley connected with the archetypal patterns behind the Kerubs and found that the symbolic map he had inherited from the Golden Dawn did not match up with them. But the trouble is that this mis-match (if that is what it is) is pre-Golden Dawn, and is woven into countless other things. To disentangle it all is obviously a big job, but I think this is one of those areas where Crowley was pragmatic and just used the symbol set he was already familiar with.
Basically Crowley knew something was wrong with the traditional sequence. He got Harris to paint on the cards. But that is about as far as he went with it. Someone else is going to have to clean up the mess called 'tradition'.
Thanks for quoting Jim's comments; they definitely shed more light on the subject. I think if Crowley had lived another 30 years he would have sorted all of this out (at least to his own satisfaction, but we would probably still be gnawing on the bones).
My astrological texts put a slightly different but entirely complementary "spin" on the Scorpion-cum-Eagle duality. Scorpio is considered to have a three-fold nature represented by the Scorpion, the Serpent and the Eagle (no mention of Man, but then Man is the "field of operation" upon which these forces work). It's an allegory about degeneration and regeneration, death and resurrection, in which the Eagle takes on the aspect of the Phoenix, the Scorpion symbolizes the self-destructive/procreative release that consumes the Phoenix, and the Serpent the medium of transmutation (watery, as a snake's movement mimics the undulation of waves) by which the Phoenix rises from the ashes (sounds like the Kundalini force to me). The Serpent symbolizes the primal urge to transcend the baser excrescences of one's nature, uniting the lowest with the highest. The Scorpion, bent on eliminating anything superfluous, stokes the flames of self-immolation (or perhaps it perturbates the waters, exciting dissolution), the Serpent, released by the consuming fire (or buoyed by the up-rushing Water), flows upward to find the Sun, the Eagle/Phoenix, loosed from its material bonds, soars into the Air, looking for another Scorpion to invest. Interestingly, although the Eagle can be a carrion-eater (cleaning up after the Scorpion?), the ancients believed the Phoenix fed on Air. These qualities echo the respective Scorpion/Man (Ophiucus) and Eagle (Aquila) correlations to Scorpio and Aquarius that Jim described. They also demonstrate consistency with Crowley's revisions to the Hierophant and Universe cards, and, to a large extent, his use of the symbolism in Death and the Prince of Cups.
Esoteric astrologers are fond of the phrases "a higher octave" and "a higher arc." Hence, Aquarius is a "higher octave" of Scorpio since they are successive "Fixed" signs placed in "Succedent" houses (a double-serving of the "established force" idea) , in a balanced arrangement on the "wheel" with Aquarius farther along the path to self-realization. Aquarius universalizes (Air) what Scorpio releases into solution (Water) through a refining (evaporative?) process. Due to the all-pervading quality of Air, the Eagle in Aquarius has a loftier vantage point and a more trans-personal (11th-house) focus than the Scorpion in its namesake sign; the latter is still crawling on the surface, involved in 8th-house matters (renewal and release; elimination; extraction of essences; sex and regeneration; restoration - in short, the pursuits of Man in his element).
Or so it seems to me . . .