I don't agree with Mirikon's interpretation here. Let's assume for a moment that
- You have two throwing knives, one of which has a touch preparation on it
- You have a way of handling the knives without triggering the preparation
- You are ambidextrous and have both knives readied
- You happen to have the same initiative roll as your opponent.
case 1:
- Pass 1, you throw the non-enhanced knife, missing your target but hitting the wall they were standing against.
- Pass 2, they pick up the knife you just threw, at the same time as you throw the enhanced knife, successfully hitting them.
case 2:
- Pass 1, you throw the enhanced knife, missing your target but hitting the wall they were standing against (this does not trigger the preparation).
- Pass 2, they pick up the (enhanced) knife you just threw, at the same time as you throw the non-enhanced knife, successfully hitting them.
case 3:
- Pass 1, you throw the enhanced knife, missing your target but hitting the wall they were standing against (this does not trigger the preparation). (same as case 2, pass 1)
- Pass 2, they pick up the (enhanced) knife you just threw, at the same time as you make ready weapon and take aim actions with a pistol, having decided that knife throwing is not for you (i.e. you don't make an attack action)
case 4: One difference, the preparation has a timer trigger, and it is going off next turn. And you both have terrible init values and are only getting one action per turn
- Pass 1/turn 1, you throw the enhanced knife, missing your target but hitting the wall they were standing against (this does not trigger the preparation). You both have terrible init, so this ends the turn.
- Pass 1/turn 2, You throw the non-enhanced knife, successfully hitting them. Also in the this pass the timed trigger on the preparation activates, casting whatever the prepared spell is.
In case 2 or 3, surely when they touch the knife, it would trigger the preparation. In case 4, surely the preparation goes off at this point no matter what you are doing. That this happens to occur on the exact same initiative pass/value as when you made an attack role is not relevant, surely? That is, it would seem to make no sense that the preparation would not trigger just because you happened to be attacking them that pass instead of doing something else.
So then, how is case 2 different than case 1, with regard to the preparation? I'd argue that they are not different at all.
But then what about the 'only one attack roll per pass' rule? I think this still follows the rules, if we assume that touch and timed preparations are considered to be their own actor. You make a knife throwing attack, the preparation makes a spell attack, each is making one attack roll. (and the same logic would apply to grenades with a timer trigger -- you making another attack action does not somehow stop the grenade from going off)
What I'm less sure of is how this would work out with voice activated triggers. My instinct is to say that the one giving the command is the actor here, not the preparation. But I'd certainly be willing to listen to other arguments.