My observation is that the treble was far too high. Setting the EQ to "Bass Booster" mostly worked, but resulted in some really nasty clipping artifacts. I'm now using the "Treble Reducer" which works much better. I never felt a need to make any adjustment on my (1st-gen) iPod Nano.

Otherwise, the only thing that's annoying me is that there's no way to set the different alerts the way I want. I want new emails to vibrate with no sound, but I want a beep and vibration for SMS. (Email is arriving all the time, and it's rarely important enough to interrupt what I'm doing, but SMS is much more rare and thus worth generating an interrupt.) For now, I just have email alerts turned off altogether.