So what exactly changes the damage?

Some of these i know changes it, some dont.

Parthy meditiation

azhidals mask

Full dragon aspect shout

aspect of terror perk

augmented flames.

Anyone know which ones are effected?

Also have you found anything interesting about how some things effect shouts? Like alteration's stability perk effecting slow time and such.

According to the uesp from what I can tell, only Paarthy's Meditation increases its damage. No talk about the others.

Of course, it's likely I'm wrong.

hmm, no you are probably right. Guess ill test it out some.