I wanted to thank everyone who has contributed so far. I have some more points I want to sketch out, but this post is intended as a sort of landmark of where my understanding is at the moment. I think only a few people will be able to judge that, but I think if I am right, those who know will appreciate it.
So....here is the thing.
This morning, I was thinking about defense and I had the feeling of receiving an attack in such a way that I just enter and crush the other guy down by bending him backward and just crushing him down to my feet. I felt this as a ki/body movement, with powerful downward crushing ki, though not using much physical effort.
So then I thought, "That must be what they're talking about in daito ryu, bringing the attacker down right at your feet."
And I thought about that for a little while and I suddenly felt, "Oh, yeah. That's the same as pi quan (splitting fist) in xing yi."
So that's where I am now, with the impression that the daito ryu drop-at-your-feet method is the same ki usage as the xing yi splitting fist, pi quan.
So who can tell me if that is true?
What if you did pi quan with a different ki usage, so that it wasn't the same ki usage as downwards crushing in DR? Would that make it not pi quan if you defined pi quan as being that ki usage? What if the ki usage in pi quan was not the same, would that make it somehow wrong to use that same ki usage in pi quan then? And if pi quan is splitting, is down really just down, or is there also an up (to split), or can the splitting really happen along any line (or non-line), and do the two directions have to be direct opposites, or even just one or two directions?