This headphone is deceptively hard to drive. I purchased this headphone because Drop mentioned that it is easy to drive due to their low impedance. Sound coming from this can with fiio e17k was underwhelming. Bass was lacking, Mid sounded so cold and treble was sibilant. It can get loud but loudness does not mean that headphone is being properly amplified. I upgraded the amp with Fiio K5pro which was as equally powerful as Atom. Man, the difference was night and day. All of sudden the sound became warm and fuzzy with more revealing details as if the new amp was puting more bodies across all of frequencies.
I was very puzzled that this headphone was harder to drive than HD6xx. I had to turn volume knob around 12 o'clcok on medium gain where 2 o'clock on low gain for HD 6xx. So the information Drop claims that K7xx is easy to drive is inaccurate.