I agree with the above -- unhook the equipment and put it inside your house (temp controlled environment). Condensation can cause corrosion, and over time it will cause your gear to fail early -- probably volume pots will go first, if something doesn't short inside the gear. Being an engineer, I used to do highly accelerated life testing, and condensation can cause much harm, even if the circuit is not energized.
Any harm in leaving gear in the cold?
I use a Carver receiver and Pioneer six-disc player, along with some Mirage Oasis outdoor speakers, in a pool side system. The receiver and cd player reside in an enclosed, unheated shed. During the Canadian winters, the temperature can dip to well below zero. Since all components (integrated circuits, caps) are specified to operate 0C to 70C, and have a storage temperature of -40C to +85C, is there any harm in leaving the gear in the shed over the winter? If I unplug the stuff, any harm done?