Speakers - according to the NRC's measurements, your speakers have a broad peak from about 750hz to 1500hz. This will overemphasize high vocal fundamentals, like sopranos, and instruments in the same range as a soprano voice and will more likely be perceived as brightness than a peak in the treble higher up. After dipping into the treble, there was also an on-axis rise from about 7khz up through 10khz and beyond from which you might perceive some sibilance or sizzle.
Walls, doors and windows reflect everything. So does the ceiling. Height of speaker stands. Toe-in. I wouldn't toe them in. Furniture. Leather and wood are reflective.
It isnt your amp. Your amp is a pretty good one to use with those speakers in fact. Nor can cables add any excess energy. Maybe there are cables that can function as tone controls in quieting the top end some, but there aren't any that can deal with the problem in the upper midrange (old school definition of midrange). I really doubt that your cd player is a problem either.
Drapes, soft furniture, room treatment. Or replace the speakers.