I think you describe the amp perfectly. Very musical, beefy American iron sound, weighty on the bottom, tighter than the ST 140 by miles, even tone across the board, the MOSFET mist is there, yet you tend to ignore it when listening to music instead of the system (and then I added the Maggie mist to it). The sibilance is preamp specific. With a very clean pre or a passive unit it goes away (perhaps a bit of tone control there), but was accentuated when I ran a DAC straight into it. A bolder, brighter, more detailed improvement to the American classic ST 140 that Sam Telig waxed over back in the 90's. I'm glad it got passed on to a person who understands her.
A couple of asides. B&K was a small operation that made running changes in product without documentation, at least public documentation. As far as I could find out, they changed the output transistors and maybe a few other parts as the model years went by. Supposedly this was on or about when they dumped the rack handles and changed the graphics. Thus proponents that say always buy the model with the handles. I haven't a clue as to the veracity of any of that, but followed the advice. Secondly they made a short lived ST202+ that increased the bias to make the amp run around 200 watts into 8 ohms, which ruined the sound and made the amp very unreliable, witnessed that it's nearly impossible to find that model yet regular 202's are often seen on eBay or A-gon.