Hi Jmone,
I suspect the sibilance is on the original recording, whether through an incompetent recording engineer or even the artist herself. The reason I cite the latter is that I was once at a reception after a concert of Holly Cole (early in her career). The vocal mike she used for the concert had a horrible presence peak that emphasized sibilance. When I spoke to her, I gently asked her about the mike and she replied that it was her "favorite" and that she used it for recording. (Her early CDs were very sibilant). Anyway, I suggested that she not use it anymore because of the grating sibilance. I presume she took my advice because later on her CDs were fine.
You can check your recording if you play the recording and listen through good headphones--just play it in stereo and see if it still sounds sibilant. If it does, then the problem is in the original recording and it's really hard to correct.
You can try using the treble control to reduce the sibilance, but usually its effects are too broad. You'd really need to insert an equalizer into the center channel and adjust the midrange controls, which might help, but you may have to live with it.
Regards,
Alan
