To be fair, the IPOD measures superbly well when driving a very high load impedance, as the majority of on Stereophile tests used as a condition in the review at subject here. This represents driving a pre-amplifier or amplifier input(s). When driving low impedance loads, such as headphones(especially those under 32 ohms), the IPOD has been shown to have problems in various areas, such as lowered bass amplitude caused by an effective high pass fiilter in combination with low impedance(due to coupling capacitors that are too small) and high distortion at the highest volume setting. I measured a Zen Extra that I used to have into all of these conditions, and it had much smaller deviation in performance, when compared to what has been shown to be the case with the IPOD into such loads.
-Chris