@jea48 - Furman with SMP will protect in both cases you mentioned.
It uses series mode protection (SMP) which has no activation time. My understanding is that they rate surge protectors for 5kV surges specifically because the expectation is that anything over that will jump incoming insulation to ground before it can enter the home. The series mode protection slows the event down long enough for the over voltage breaker to trip if still needed, such as the case in a continuous over or under-voltage.
I want to point out that we’re deep into the "what if" situations that are not the major cases. I remember when seat belts became required by law, everyone focused on "what if a plane lands on my car? What if a dinosaur swallows my Eclipse? How is the seat belt going to help me then?" despite the fact that seat belts converted about half of fatal car accidents to non-fatal accidents.
Living in South Carolina near the ocean I’ve had at least a dozen serious surge events some of which were near-misses but most were not. The OP has already discovered that the 2 devices not surge protected in his stereo were what went, I’ve had the same happen here, but with a laptop. I’ve also had my Furman’s turn off due to over/under voltages caused by nearby transformer events.
You are right though, the A’gon poster who had the roof blown off his living room was probably not going to be protected. How many of us have actually had that happen vs. the more moderate cases?