Thanks for asking. Yes; I did finally track down the sibilance to an unexpected source -- cement pavers I had under my Target stands. An easy fix and what a relief!
I’d also had a fatigue issue that I traced to my (Burr-Brown) Aqua DAC, which I sold. In its place, I began using the onboard (AKM) DAC in my Hegel H390. In the process, I lost some highs (the Hegel DAC is somewhat rolled off) and some bass extension, as well.
I was able to get back some of the bass with an ac cable upgrade but still need to work on restoring the highs without reintroducing fatigue. I recently auditioned a Mojo Mystique XSE DAC but it sounded very dull in my system. It would appear I need to try a less warm-sounding DAC.
That’s where things are at, currently. The system is emotionally and physically engaging but too dark.