My ZX1 has about four hours on it now. A few thoughts.
-Initially I found its sound comparable to the iPhone 5s out, using the akg 3003i. (which is not a bad thing). I went back and forth between both several times and finally decided the Sony won by a small margin.
-having physical buttons for pause, play, volume and ff/r is now essential to me. (the Tera dropped the ball not offering pause, I now use pause all the time).
-the player is sexy as hell.
-whomever designed the accompanying case should probably be fired. No button access?!?
And then I turned on Clear Audio+.
Wow. I usually say 'headstage' when discussing headphones, but with Clear Audio + on, it is that much closer to a speaker experience. There is definitely a volume boost, and I have gone back and forth with CA on/off with volume adjustments. No matter the volume, without Clear Audio+ on, after having listened to it, I can not go back to not using it. Anak & Mim, have you tried it?? I would be very interested in your impressions. The only downside for me so far is a questionable loss of midrange presence, but I need more time to test.
The th900 directly out of the zx1 is more than impressive. It's overall performance approaches what I have with my iOS/m8/tu-05 combo. (but only with Clear Audio+ on).
I have a WM line out cable on the way so I can use the ZX1 as source for the tu-05 and will report back. But in the meantime, with both the 3003 and the th900, the ZX1 does a phenomenal job.