wow. holy thread brought back from the dead.
you should still be able to hear sibilance. it's between 6khz and 10khz, i think.
here's a test track i use:
"don't look down" by lindsey buckingham. when he sings "diamonds in the sunset", every S can sound harsh, depending on your set-up. with a treble-hot system, you will just about rip your headphones off.
but, with a more laid-back treble system, the S sounds are nice and soft.
also, some singers are more prone to sibilance than others. diana krall and richard thompson can create some pretty hard S's. hahaha.