I have a couple questions about how Ausetitha, Staff of Dark Flame, and Ahmotep interact.
If I use the second power of the Staff of Dark Flame, does that apply the +/- 5 of Ausetitha? The heart of that question is whether or not modifying the difficulty of a combat check counts as being played on a check.
Auesitha only cares for you playing favored card type, so it makes no difference if it's the first or second power - you can apply +/-5.
However, since Au also says "YOU MAY" - applying the modifier will count as playing an Ally on your check (as opposed to: if the "you may" was lacking - you would always either add or subtract 5 when playing a weapon - this would be continuous effect, not dissimilar to a scenario power, so it wouldn't count as playing the Ally)
Finally, applying an effect either is or is not "playing a card" - it doesn't matter if you're adding dice, adding modifiers, or reducing the difficulty
Also, can I use the second power to reduce the difficulty of my combat check, and then play it or another weapon for the combat check? The Pathfinder Adventures digital game lets you play Wand of Ennervation and another item on a combat check, but since that's not actually made by Paizo, I didn't want to assume it was correct.
You cannot. You have already played a weapon on your check, by revealing the SoDF in the 'Determine Your Skill' step; therefore, you cannot play a second weapon by revealing the SOTF for its second power in the "Modify the Check' step.
(There was a recent discussion about whether playing the SAME card (i.e. SoDF) in different steps constitutes playing ANOTHER/DIFFERENT card. I do believe the consensus fell on "Yes, it does", but you may search for the thread if you're curious)
If the Wand of Ennervation works like you say in the app - that's a bug. Maybe the other item had a power "You may play another item on your check"?