I've had these headphones for quite awhile now and been very happy with them. Listening to pop or electronic music have been very enjoyable. However, I've noticed that the headphones perform poorly with quiet sounding tracks or instrumental solos. Its the most noticeable at low volumes. Sometimes, the headphones will fail to play some of the very quiet sounds that my Etymotic HF-5 have no problems producing. Additionally, a pervasive and annoying hissing sound can be heard throughout the track along with an unpleasant resonance (not an audiophile so don't know how to succinctly describe it). Even at normal or loud volumes, the same hissing and resonating sound can still be heard.
I was hoping someone could try to recreate the problems I am having in order to know that I am not the only one facing them. Here is a track from my music collection that might better help illustrate what I mean.
Try listening to it at low volumes and then at normal or high volume.