Originally Posted by TexasRockbox
There's quality and then there's capability. The perceived sound quality can be affected (in part) by poor impedance matching, sensitivity of ear device and output current. The trick is to get a good match between player and ear device.
I get what you're saying, but its worth remembering that headphones are not (and should not) be impedance matched. You want much lower impedance on the device then the headphones, which is why low impedance headphones tend to be harder to drive.