Paul G asks:
"[W]hat is the best way to protect a
speaker from destruction if the amp is sufficiently powerful, and you
have no control over volume? It happens.... the kids have fun with
your stereo, the grounds come loose on the inputs (huge buzz), the
system oscillates, etc."

I don't know if you want to design and build your own stuff from
scratch, Paul, or merely want to buy a plug-in protector. If you can
solder, here's a halfway house in a couple items to protect your
loudspeakers from switch-on pops and from DC.

Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay

Velleman K4701 Loudspeaker DC-protection, mono

The reason I've identified them is that I have a QUAD 405 MkII which
occasionally eats an ESL-63, which soon gets expensive, and it is
tricky rebuilding them because here is no way to solder except over
the fragile panels... So an audiophile's fancy turns to ripping out
the 405's inadequate clamp circuit and replacing it with industrial
strength protection.

The reason I choose Velleman is I've built some of their kits,
including the multimeter I've used for years and a 100W PP tube amp,
and found their stuff first class, head and shoulders above the
competition (well, in most cases there is no competition, because the
other guys make crap); in the end Velleman is worth the premium price.

Andre Jute
I just listen to one channel at a time. You do have to listen twice.
Adequate stereo separation. -- Al Marcy