I've also been trying to unravel the aces, been drawing them a lot lately, as 'centre'cards (theme/situation, upcoming event).
For now I've had the Ace of swords mostly come up as communication of some sort; this could be an (job)interview, a serious talk/discussion, or even a police interrogation.
The Ace of Cups had actually come up once for a 60+ woman who was having emotional/ low-confidence issues, because of aging.. it was in a reading with, 6 of wands and 8 of swords and the World.
The ace of cups+ World represented that (life)cycle...
When I first saw the Ace C I Thought whats it doing here, its normally a nice card to see right?! but I could feel something 'negative vibe' in the reading...so my first thought about a possible negative interp of the Ace was 'heavy emotions'... in the 8 of swords an 6 of wands we discovered why..lack of self confidence.. (so these aren't 'positive' emotions)
Ace of Wands has come up as sex(ual energy), but also as a lack of sex(ual energy) with other certain cards.
I usually see the Aces as good cards to have, but they can represent so many things, even turn out to be not so positive or just be there as additional info to another card.. So in my readings ( and the way I read cards) it really depends on the other cards, and its position and the question asked.... I dont do rx cards so i always turn to other cards for info first thing ...and sometimes I'll do a raeding on the Aces potential itself and what its representing or how I would recognize such opportunnity.
the Ace of Pentacles is still under investegation