[shigzeo]

I'm a big fan of the zO2, but I listen at normal levels. Every amp will hit a limit when reaching huge volumes with certain headphones. The zO2 is an external EQ and amp and it does both very well indeed. At normal listening levels the Pro 900 will NOT distort like that. The amp circuitry of the zO2 isn't as robust for high volumes, but then again, who listens at over 95dB? Or, if you do, why?
 
EDIT:
Just sounds like you are overloading the input on the zO2. Back in my concert taping days, I had to get an external low pass filter for live recordings as the bass from concert subs would sizzle in the mics. The Fiio may have a more robust input system and that is it. Output, the zO2 is hard to fault. But then again, the 24dB of output from rock box on a clip leaves something to desire.

 

[Makiah S]

you may have a point, it's hard to tell unless I could actually listen to both of them through some DARN good cans.
 
Still though with the E11 being cheaper z02 is a toy for later down the line I think!

 

[WakiDabeast]

from my experience with the Z0 it works very well for some headphones and then works only as a bass contour for others, on my HD25 the sound doesn't improve, simply becomes smoother, but on my M50's the sq actually improves as well as good use of the bass contours ^^. I think just in general it smooths headphones out, but it reaches an "assymptote" where a headphone is so smooth that the Z0 won't make is smoother......... I'm half asleep right now sorry if that was all just mush to your brain cause it crystal clear crap in mine 

 

[Prakhar]

Mr.Nurse
What EQ settings do you use on your clip for the hfi580?

 

[Serotonin]

Sweet jesus, I just got the ZO2 with my pro900, distortion city @ high gain and @ mid gain it middies up everything else ;( 
E17 def does a nice job of controlling the bass even at high volumes but I am going to compare it next to E11 tonight see how it does. 

 

[Kites1080]

Check out the reviews on the Encore mDAC.
Its a dac/amp
Half the length of iphone 5
Double the thickness
So its very portable
Reviews are excellent

Selling for $130 on amazon at the moment

 

[Kites1080]

Also shozy magic portable. Of similar size to encore mdac. But cost is around $480.