In terms of left,right, front, back, up and down - I have always thought of it as the x, y, and z axes in 3D. And my way of analyzing stuff - well, for movement I like to think in 8 directions. So, when cutting with a sword, I like 8. But sometimes, 12, like a clock - because I want to be able to attack and defend from all directions, and you can only do that if you practice it. I think you can do whatever you like, as long as you do something. But for balance and body structure, both of the self and of your partner/opponent I think 6 is fine as it is just - logical.
I can't see how it is directly related to zanshin though. You do need to be aware/awake/alive, of course, always.
Just be aware, it's not movement (in space, external) here that's being looked at. Like Cady said, it is intent, that happens solely within the body-mind before any external movement has been involved. And the fact that it is called "6 directions" does not even mean that those are the lines we are actually initially working with, think of it just as a descriptive allusion, i.e. the cross-lines of fascia through the body, motivated with intent, can effect horizontal and vertical stability and are initially more important than any lines that would actually run horizontal on some imaginary 6 direction compass.
Thank you, Rupert and Cady! Very cool!
As for zanshin, I think it was the idea of 360 degrees (omnidirectional/spherical) awareness that caused the association.
I can see how they wouldn't necessarily be the same things; I'm guessing perhaps zanshin refers more to a mental state than a mind-body state? Being "in the moment" as opposed to being able to absorb and redirect (or whatever) instantly?
It is also possible that our understanding of zanshin was backwards all along. Rather, once we learn IP, we learn maybe our zanshin needs to draw more from our IP than our IP from what we may have mistakenly thought was our zanshin.