Off the top of my head, Accuton or Seas Excel come to mind for the mids, and the Millenium for the tweeter.
Been there and done that.
The Accuton is debatable and would depend on the implementation. I have used the Seas Excel drivers quite bit and would not put them over the drivers in the X-Statik. The metal frames tend to ring a little and the metal cones have a very unnatural sound to them. They sound artificial next to the X-Statik drivers and if not crossed over very steeply have a terrible ring to them.
I have also used the Millennium tweeter several times and really can't put it over the X-Statik tweeter in any way. And I like the way the rear wave is controlled better in the X-Statik tweeter. And I think the Fs is lower in the X-Statik tweeter too.
If you really want to see a step up over the X-Statik, then hang in there for the long awaited X-Optima and X-Otica. I have something special in the works.