Hi,
as I read the responses here and your original post, it seems clear you should have a protected outlet at each speaker
An inexpensive product with an equipment warranty would be the Pro series fromAPC one for each speaker total of around $60 or less
if your house wiring is correct, and you have a surge, the units *clamp* the voltage, fail the unit in off mode. replace with another or send unit in toAPC for replacement
message me if you need more detail, or would even like a call to clarify.
hope your repair goes smoothly!