Thanks ClieOS for the review and constant updates of this project.
Finally able to demo a production unit today and I am blown away. Sound wise it is at least on par with AK100 and with more power - drive my ER4S at 65% volume vs over 85% of Ak100. Very high level of detail retrieval and clean sound. Separation and imaging is slightly better than AK100. FR is quite flat more akin to dx100 but very slightly warmer. Wasn't able to a/b with AK100 or Dx100 as I was listening to my AK120 when I ran into the demo unit. This made me even more impressed as the X3 is not dwarfed by the way more expensive counterpart on sound. AK120 is definitively better, but most won't find the price difference reflect the improvement of the sound itself.
Big thumbs up to the Fiio team in delivering superb but affordable sound.