Mentioned here: https://cgi.ikmultimedia.com/ikforum/viewtopic.php?f=12&t=19885&start=90#p107938
quick follow-up... Microsoft recently released a Windows system update to undo the damage caused by a previous Windows system update. (Sadly, this is not a joke.)
I installed the "fix" update last night. The issue with crackling sounds when I play lots of notes on high-memory pianos is gone.
Makes sense that it was a system issue, as I have a fast enough processor and enough memory that I really shouldn't ever have that kind of problem with ST.
I'm guessing there are other source problems for other users, but at least on my system, it's resolved.