Here we go again with the Hi-Res moniker but sagging FR below even 20khz. I'm not sure if that's once again your soundcard or the Fiio's DAC or amp.

@LajostheHun - actually thats the DAC on the X7 - nothing to do with the amp section.  And if you check most high-res players, they'll all have that roll-off.  Even the $1300 L&P LP5 has it.  You can check graphs of some others here (bottom of the review) - http://www.head-fi.org/products/fiio-am2-medium-power-amplifier-module-for-x7/reviews/15278
 
And it has nothing to do with my equipment - FiiO shows the same measurements on their website.  it simply has to do with understanding low and high pass filtering, and what sounds good to the human ear.

I wasn't "accusing" your equipment here you simply mentioned something about it regarding another measurements you took,so I was rather "fishing" there.
As for the intentional roll off ,is just hogwash it has nothing to do with "understanding" filters but rather how they intentionally manipulating or "tuning" a signal that should rather be linear or "transparent", and there is no universal" what sounds good" to the human ear, that just varies greatly by listener . I do realize Fiio isn't alone in this which is why I said 'here we go again" it was not a knock against your review at all, which I always appreciate.

You asked the question - I simply answered it.  Its not the amp, and its not my equipment.  its the DAC on the X7. Its clearly shown on both FiiO's website and on my graphs.  As far as the Hi-Res moniker goes - I was merely reporting on the package - and it evidently meets the requirements of Sony's "High Resolution Standard" - which (if you want my honest opinion) is a waste of time anyway. Even the best ears can't hear above 22 kHz, and we can already reproduce the audio signal perfectly at 16/44. As far as the drop off goes - TBH, I hear very little difference between the perfectly flat E17K and the gently rolled off X7.  One is a little warmer/smoother than the other. Both sound perfectly fine to me.