first, in order to have stacking work properly, you need to set that last line to 'TRUE'. Then, you change the stackingLimit line to the amount you want (we'll say 50). Now, you change the first line from 'PrioritizeOldBuffs' to 'PrioritizeNewBuffs'.
There are other options for buff prioritization values for that line, but those are some basic ones.
Also, after looking at the BuffEnergyWeapon and BuffEnergyWeaponSelf (the buffs used by the Halcyon's Energy Aura ability), I am not sure why you would need that ability to stack. It's a passive, so no matter what as long as something is within range of the Halcyon's ability (w/in 8000 arbitrary game units), it will have the effects of the cooldown. So why do you want this ability to stack?
Ah, NVM, I see you used that ability as the example. Well, what you probably want is for it to PrioritizeNewBuffs, and just set the stacking limit value to a finite number.
However, many abilities that stack have an infinite stack or they do not stack.