Many thanks for those kind comments. I'll just add something else I've discovered. Just for fun I decided to try measuring the EQ of the sound coming out of my Audeze LCD-4 headphones. So I put the flat of my hand over one of the phones and poked my trusty UMIK-1 condenser microphone between my fingers, pointing at the driver. I then recorded a track of pink noise from a test CD. Here is the frequency response I obtained (using Voxengo CurveEQ): Now, I would the first to admit that my measurement method was a bit hit-and-miss. But most of the chart looks quite convincing, and the most striking thing about it is that there's a simply enormous notch in the frequency response - about 20 dB, using the scale on the right - at about 4 kHz, which is exactly the frequency that's the cause of all my problems! No wonder my ears LOVE these headphones - they could have been made for me. I tried applying this EQ curve to playback through my ATC SCM11 speakers and it does indeed fix the vocal distortion I'm hearing but it takes too much other stuff away at the same time so I don't see it as a solution. It does, however, explain why I'm not getting this problem with the Audeze LCD-4 headphones. Now, if I can just find a pair of speakers with a notch like that.