Cold room, Bad for equipment?

I'm a very fortunate guy in as much as I've recently finished transforming a gutted detached garage into my dedicated listening room.After 1.5 years and hundreds of personal man- hours I am putting the finishing acoustic panel touches and tweaks and finally enjoying the music. It is extremely well insulated with R-13 insulation between the studs and a layer of both 5/8" drywall over 1/2" quiet rock all around, except for the ceiling which is only 1 layer of 5/8" and the R-13. Floor is carpet over laminate over Dri-core, so that's not a problem either but I live in NY and due to the added complexity of an HVAC system, I have not added any heat to the room.With winter temps dropping to less than freezing I'm wondering what is considered a minimum temp I should try to be maintaining through the use of portable space heaters in order not to be harmful to my equipment. This includes a mix of some units in stand-by mode (my tubed pre-amp with low voltages keeping them warm) as well as CD transport, Dac, and self-powered sub woofer which are always left on. Amps are left off of course, both a big solid state Classe monster as well as a tube amp.My in-room thermometer has read as low as 50 F tonight and the space heater brought it up to 60... Obviously the amps will warm things up a bit while playing but the big question is how low can I let that temp go without doing any possible harm to anything???Note there is 1 30"x60" window with blinds and a 3/8" piece of sheetrock pressed up against it (from the inside), effectively sealing it closed. The one door is a standard"outside" door with a separate glass storm door outside of it. The original 'car' garage door has been sealed and a new internal framed wall (sheetrocked as the others) is in its place. Thanks in advance.