Do Plinius amps have high frequency anomalies?

I have Shahinian Hawk speakers. I have tried driving them with two different models of Plinius amp and they both had an effect on violins and trumpets and sometimes voices which I would describe as "electronic." I perceive the area of principal coloration to be in the sibilance range and it seems to add a slightly whistle-like character to the sound, especially at high levels. On some (maybe rolled-off) recordings, this emphasis can be attractive, enlivening the string and brass sheen that occur naturally; but on most cd's and lp's, the effect is not to my taste. The two models I tried were the P-8 and the SA 100MkIII. The latter was the smoother and more realistic sounding but they both exhibited this coloration I am describing.
I am just wondering if any of you have experienced this with Plinius amps or if any of you who have heard Plinius amps would like to offer commentary on their high frequency performance.