Thanks, all. The speakers are still in the garage. I put many peanut butter laden traps all around the speakers, but haven't caught anything yet. I'll take the woofers off and see if I can see any damage and try to clean any mouse house remains.
I live in a relatively bucolic area, and it's a constant battle between mice and us. I made a mistake by not plugging the ports, but I didn't think about it.
As for cats, alas, the wife is allergic to them.