Just heard the Amphion Argons and have a pair of Zu Tones on home audition. At the moment anyway, I'd give the Argons the nod on voices -- more transparent and open, though the Zu folks tell me that my Tones need more time, and the slight thickness I hear in the mids will take care of itself.
The Argons are very nice, though I did hear some timing discontinuities that you don't hear w/the Tones -- they have a really inviting dynamic flow. Am inclined to keep them if the midrange issue I hear fades, they have a lot of strengths. I would, however, ignore all claims of 'blowing away anything in their price range', etc. These are silly statements as there are obviously a lot of talented speaker designers out there. There are, for example, things I like about my VMPS speakers better than the Zu's.
Incidentally, Zu is far from the first speaker to have no crossover to a driver. Epos has done this for years, w/a simple circuit to include the tweeter, others have/do as well.