I think the AK is edging it for me to be honest. I like the fact that it will probably be powerful enough for use on the move. Ideally I'd just like to carry around a DAP with no amp connected to it.
I've just been reading about Sony's recently announced ZX1. Although yet to be released this sounds like it could be a great DAP, so long as they get the sound right. With this in mind, I may wait until this is released before making a final decision.
I'm also thinking of upgrading my Future Atrio and getting the Westone W4R, so that may influence my decision too. How my wallet yearns for me to stop visiting this forum. Lol
Have you considered the dx50? It is only a little bigger than the ak100. It also has a built in amp. The sound isn't as clean as the ak, but people tend to like the dynamics. It is also a lot cheaper, less than 300 shipped. I would wait until they work out all the bugs in the firmware though.