Don't think so. I'm aware of the 6 Harmonies concept and I think you're right about it having more to do with spiral power. But it's not what I'm talking about above. What did I say that made you think so?
It just came to mind when you wrote: In my understanding, this circle of opposing powers is exactly opening in 6 directions, which is silk reeling. So, according to the founder, this skill is at the core of aikido. And it's the basis for creating in/yo, dual opposing spirals, putting Iganami in the left hand and Inazami in the right, and standing on the floating bridge of Heaven, all of which he also said were the basis for Aikido, but go read Chris' blog to find out how.
Maybe I'm just reading it the wrong way.
(Internal) spiral power certainly is part of the core of Ueshiba's aikido; the 6 Harmonies, as I understand them, involves the mechanics of that process, while "6 directions" is more or less our (we folks on the "aiki bus") shorthand for working the In/Yo process of building structure and laying the fundamental groundwork for making IP 'n' aiki.