Ok, the sibilants I was concerned about are certainly real. There are quite a number, but they are generally in the lead (unaccompanied) vocal sections. They are slightly unusual in character, as I'd describe them as a small and very sharp beak, with tons of energy around 6-8K.
Color forms unTTer your cheekSSSwhen..inTTentions..hard TTo know TTan acTT of reason..and so on.
Since this is such a first class work, I'm tempted to suggest fixes for things that would pose no concern in a lesser quality production. The nylon string that opens the track: It was tracked with piezo and microphone, if I am correct. What I believe is the piezo tone is a detractor, for me, and is much more apparent in the opening passage, when the acoustics are naked, than elsewhere. Changing the ratio of piezo to mic might work. The piano during the mini-breakdown at 1:33 sounds very nice. You might use that in the intro section, alongside or instead of the nylon string to mask the piezo plastic timbre. You have acoustics doubled and wide panned there; so perhaps one acoustic, and one piano. Just a possible approach, of course. If you love the tone of the acoustic, then disregard entirely.
Keep us posted on this and when you'll be releasing the track.