If you are into planar magnetic headphones, and find that they do indeed reduce harmonic distortion when compared to the dynamic drivers found in most headphones then check out the FiiO FT5. They are open backed planar magnetic headphones with a 90mm driver paired with a 6 µm thick polyarylate diaphragm that sport an impedance of 36 Ω and sensitivity of ~96dB/mW. They also have an impressive 7 Hz–40 kHz frequency response range, if you can hear notes that low.
As with other planar magnetic headphones they are a little heavier than normal, 456 g in total and for some reason the headband is designed for relatively small heads. If your head does fit, the wide self-adjusting suspension band helps with that weight quite a bit. As for how they sound, check out TechPowerUp’s full review.