Channel Harm

Two 3/3 creatures are attacking me, I cast Channel Harm targeting each and then let them through unblocked.

I'm the affected player and I choose which prevention effect to apply first.
Do I get to choose the order per source? ie. is each considered a different event within the turn-based action of combat damage?

Intuitively, I think it should be per source, otherwise, Timmy the Rules Noob is going to be in for a surprise when one Channel Harm deals 6 to one of the 3/3's and the other deals nothing.

edit1:
As precedent, it occurs to me that two Empyrial Archangel likewise let you choose which to apply per source so I think I have my answer.

edit2:
hold up a minute - http://www.cranialinsertion.com/article/197

Would the result be different if I blocked one of the 3/3's?
Now that damage that would affect a player and an object, I'd get to choose the order of application distinctly for each, right?

Edited Todd Bussey (Feb. 3, 2015 10:47:10 AM)

Since combat damage is simultaneous, there is only one instance of the event “damage (being) dealt to you and permanents you control (…) by sources you don't control” to be found. When you apply a Channel Harm to that one event, it will prevent all of the applicable damage, leaving none to be prevented by the other Channel Harm.

As such, one of the 3/3s will be dealt 6 damage by the Channel Harm that targeted it, and the other will take nothing from the other Channel Harm. It doesn't matter if one or both of the 3/3s is blocked.

Edited Callum Milne (Feb. 10, 2015 02:05:22 PM)