I have a pair of M3s and have a somewhat similar experience. I have M3s driven by a Yamaha HTR 5730. I listen to music only. I Have Joss Stone's CD "Soul Sessions". On 1 or 2 of the tracks, I can't remember which songs. She hits a couple of notes that, IMO, don't quite fit. They are hard to listen to. I would say they are "shrilly"-not quite distorted. I have played a ton of music on these beautiful M3s with no problems-even at loud volumes. It just seems to be a couple of notes from 1 or 2 songs.
I just keep telling myself it's the fault of the microphone that she recorded the CD with!
Ill be interested to see what you come up with! Good Luck!
