Absolute top-notch build quality, even down to the included cable. Excellent bass and transient reproduction, good imaging depth. Wipes the floor with my old AKG Q701's. I was shocked when A/B-ing them how muddy and indistinct the Q701's sounded by comparison.
Also easy enough to power with the built-in headphone amp on my MOTU 828. I never really need to take the gain above -10dB, so there's plenty of headroom to work with. Sadly I don't have a high-end headphone amp to compare against, so I can't comment on distortion other than to say I don't perceive any.
The big negative is that these things have way too much treble out of the box. To match the Harman EQ curve I needed to cut 8dB(!) above 10kHz. Without EQ they're both fatiguing to use and untrustworthy for mixing because of this.
The rest of the spectrum is fine, though - they don't need more than about 2dB of boosting or cutting anywhere else. They take EQ well, and once corrected to the Harman curve, they make a great mixing tool. I have extremely good monitor speakers but my room acoustic treatment is limited, so these are really handy for checking low-end and imaging without the influence of the room. Glad I forked out for them.
