Thank you for answering, I was wondering about getting no response.
Well, I didn't reply earlier since I never saw your post until yesterday.
In my thinking, if I have two effects that both are free actions or trigger on the same thing as free actions, I can choose which of them to use when.
Well, that's a different rule than the one you mentioned.
You indicated that item properties worked before feat triggers in your earlier post.
If you have two powers/actions that occur simultaneously, you can choose the order in which you resolve them. Not sure where that's written down bit I'll try to find it.
It's in the Rules Compendium and is a new rule (since the PHB).
But, it is only on your own turn (AFAICT). There is no such rule for during anyone else's turn (e.g. the warlock gets a handed a free ranged basic attack, bloodies a foe, etc.).
Here's the tricky part though.
The Dark Pack boon is listed as an Immediate Interrupt action, not as a free action.
So, the RAW interpretation of it is that the Effect is an Immediate Interrupt that cannot occur on the PC's turn. Just because other pact boon triggers are free actions does not mean that this one is. It's an II to get an aura point and it's a different II (for the trigger) to use them. Given this more RAW interpretation, the item wouldn't stack with the feat because one cannot do two IIs in a round.
Now, someone could claim that the Trigger is the II and that the Effect is a free action (because of how other pact boons work). For other pact boons, the knocking to zero hit points is a trigger which happens to be a free action. Here, the knocking to zero hit points is an effect. It might be RAI (every time a foe drops to zero, the aura gets a point, even if it's on the warlock's turn) and I agree that this is a reasonable interpretation, and this is how I would interpret it.
Given that, though, the trigger of Darkspiral is doing the damage, not adding the aura points. So the rod wouldn't give an extra point to the spiral because the rod only allows the trigger to fire off. The trigger for Darkspiral is NOT the effect.
The trigger for Darkspiral allows for a hit. So combining the rod with darkspiral aura and the feat would technically mean that the PC on his own turn could bloody a foe and wound that same foe with the aura with the same attack.
Now, it gets better. Since these are free actions, they get resolved like Immediate Reactions.
1) If the rod occurs before the feat, then the damage is done with one fewer point in the pool. The Special (which could lower the pool to zero) occurs, and then the feat would raise the pool by one.
2) If the feat occurs before the rod, then the pool is raised by one and the curse is removed. The rod then does not trigger because the target must be cursed.
So, choose your poison.
But my earlier interpretation of 2 points from the warlock bloodying the foe wouldn't be correct. The rod explicitly states that it only affects the trigger of the pact. This also means that none of the vestige pact boons would work with it because most (if not all) of them do not have triggers.
Your pact boon triggers when an attack you make with this rod makes a target affected by your Warlock’s Curse bloodied. (It still triggers when you reduce a target to 0 or fewer hit points.)
It's apparent the that designers of this item were thinking of the other pact boons where knocking below zero IS the trigger and is a free action (which means it can be done on your turn).