“i currently have a parasound a21+ driven by a cary audio SLP 05 tube preamp.
i liked the parasound at first but after 7 months or so it is sounding slightly sibilant and less refined.”
I’ve had a Parasound A23+ for well over a year now and it’s not sibilant at all and I do find it refined in my professionally calibrated system. I tried a high end Class D Gan amp recently, and the Parasound was light years better in every way. Perhaps something else in your chain isn’t up to par, misadjusted or maybe room acoustics are bad.