Crack is really intended for headphones with an impedance of 300 ohms and up. You might get by with headphones around 150ohms. But the planars tend to be lower than that and our intention is that planar cusomers use the S.E.X. amp. We have put effort into offering a range of headphone amps that are optimized for various types of headphones - Crack for high impedance cans, S.E.X. for power hungry lower impedance headphones like planars, Mainline for reasonably sensitive premium headphones of all impedance ratings, and Stat for ES headphones.
