The D7000 has very low impedance, which always misleading people it should be good enough driven by any portable device. From the experience on many low impedance headphones, this means require much more power current from the circuit of amplifier. If the design of the circuit doesn't have this be considered, the sound will getting worse. Therefore, in simply say, such low impedance headphones are easily to be driven, but difficult to have best sounding. If you have the D7000, you can notice a huge difference between direct driven by a portable device and a desktop amplifier.