"The treble became brilliantly sparkling, with no trace of sibilance..."
"Sibilance" is a not very often used form of the word "sibilant" - making an "SH" sound or a "sssss" sound. So the mod removes the high frequency content of your audio so you can't hear the "sh" or "sss" in words? How can that be good?
Or, is he throwing terms around at will without the bother of having to really express any real meaning?