Well, rolling each hit separately is the only thing that makes sense. Since you can have multiple auras of the same type but different levels across your equipment at the same time, rolling each separately is the only logical choice.
Plus, I had someone look into it a month ago (Raze?), and the result was that each hit only launches one "aura sphere," at least visually, but that the sphere can have mulitple separate "auras" in it, if you look at the battle record log (it could hit with 2+ enchantments' worth of damage hits).
That's enough for me to consider that each enchantment is rolled separately when triggered, so 6 static charges mean 6 rolls to activate, and up to 6 hits of damage launched.
Also, don't forget that (I think) Destruction affects aura damage.
