Ugh. I'm ill and groggy. Let me try and explain nevertheless.
First, the animation system. You will likely know that there are more than 255 possible animations. But the animation index only goes up to FF(hex). How does FF7 work around this? By adding an offset to the 'relative' index, depending on the 'class' of attack used.
Let's say, that items have nothing added, and spells have, I dunno, 60 added.
So, the relative index for Potion would be zero, and the relative index for Cure is zero too. The 'absolute' indexes, respectively, are 0+0 (=0) and 0 + 60 (=60).
If you changed the relative index for Potion to sixty, though...
(60+0 = 60) ... it would look like Cure.
But I can only use a rel. index of up to 255. If I want to use the animations beyond (255+0) - say, the animations of enemy attacks, I need the game to properly use spells (up to 255 + 60), not just items.
And WallMarket does just that. Go to Initial Data > CharacterGrowth and change the attacks used for each limit to spells. Let Sephiroth use one of the 'empty' spell slots for his limit. This will allow you to access everything but limit and item animations.

Now, use
my spreadsheet to find the relative index for the spell / summon / e.skill / enemy attack anim you fancy.
A caveat, though - F0 / DE (depending on the version) is the Heartless angel anim, but the 'angel' model won't appear unless you're on disc three.
Now, if you'll excuse me, I'm going back to bed.
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Now, a technical discussion - do we yet know if item anims come before limit animations?