For a shockwave-based system, I'd rather have it extend off of a damage event that checks for the Sonic damage type and runs the on-hit events when a given unit is affected by the shockwave. The special effect itself could be amended in Object Editor for a minimalistic approach.
Damage types are mapped here:
REPO: Mapping Abilities to their Damage Types . The only consideration to ensure is that the casting unit does not have any other spells that deal Sonic damage that could confuse it.
The end result is much smaller triggers and a much lower overhead.
Such a system wouldn't work on older WarCraft 3 versions, but since you are using the new Special Effect natives anyway, it wouldn't change anything about the requirements.
