Sibilance is quite the problem, and some folks (myself included) have a higher sensitivity to that noise.
However, my investigationd into this has shown that it is very commonly recorded into your source; this is a resonance effect on key constanants which results in a 20-40db spike in the 4-8kHz range (you can see it easily on a frequency spectrum). Some singers have a more pronounced 'sss' than others, some use the 'vowel enunciation' technique when singing, others use mic. technique. So the origin of the problem is usually the recording.
However, if you then look at the frequency spectrum of many headphones, you'll notice that the spectrum is generally not flat, and many have a dip in the 3-5kHz region, which specifically helps 'neutralise' some sibilance. I have seen some cans with a positive bias at the sibilant frequency, which would make matters worse.
In conclusion, if your sensitive to sibilance, pick a headphone that has a dip (or recessed highs) as this will be easier on the ears. I find the HD 650 excellent, whilst my Ety ER 6i are very fatiguing.