Will audio gear be ok in unheated house

I don’t think any of that equipment will be damaged in any way. I’ve left some good quality equipment in an I heated storage unit w/ no issues at all; speakers, turntable, electronics. It’s rapid changes in temperature that can be harmful, not slow steady ones within the temperature range your house will experience. 
 

As previously mentioned, by far the most potentially damaging thing you can do is turning on equipment while it’s still very cold.  Any moisture that might be present can get quickly heated by some components like resistors, transformers etc & then condense on a nearby cooler component & then short out. 

I experienced this first hand many years ago when I turned on a TV that was out in the garage on winter & a small fireworks show ensued. Lesson learned on a fortunately a piece of junk. Lesson learned. 
 

I own and rent cottages in one of the most inhospitable temperature-wise places in the US. Temps regularly hit -20F in the winter.

I also own a house (that I occupy) on the property.

I have left lots of equipment out in the barn over the winter. Obviously not my high-end stuff, but lots of CD players, extra preamps, as well as TVs, spare electronics for both the main house, as well as the cottages.

I've also owned boats which had lots of expensive electronic equipment in them (radar, GPS, radios, depthfinders, etc...).

All have been fine over the winters, just let them acclimate before turning them on.

Do NOT put your stuff in a closed closet with a space-heater and leave it unattended. The light-bulb thing (incandescent) is fine (I used to do it in the bilge of my boats, mostly to keep the bilge pumps from feezing up), but that's only going to do so much if the temps REALLY drop.

You state you've been leaving your speakers over-winter there, so no need to worry about the finish on them (cracking veneer, or what-have-you).

I have lots of direct experience with this very subject. Take my word for it, you'll be fine. Manufacturers ship their equipment sealed in plastic bags with silica gel packets as a desiccant. That equipment usually crosses the ocean on a freighter or in the unheated cargo hold of an airplane.

You'll be fine.

As others have said, capacitors may be at risk if frozen. If any components have printed circuit boards, there is also some danger from solder spiders if the humidity and electrostatic charge is just right. Not an issue with point to point wiring.

Recommend that everything be disconnected; remove all power cords and interconnects. Wrapping/sealing is a good idea. When returning, after unwrapping/unsealing allow to acclimate at least 24 hours before reconnecting and repowering. You may also want to deox all the connection and power contacts. 

As a dealer. we received shipments from all over the world, 12 months out of the year. I recall unloading trucks during sleet and snow. These shipments were in transit for days from another part of the country, often spending their nights/evenings stored in unheated trailers. There were also days when the ambient temperatures reached over 100 degrees. A trailer in direct sunlight would have pushed this temperature up considerably -- 130 degrees, plus?

Normally, these items would have plenty of time to adjust to room temperature before put into service. But, I have to admit that when highly anticipated products arrived it was like Christmas morning -- packing material flying everywhere to get to the good stuff inside. Followed moments after by an extreme demo to see what they can do.

Back in college physics we learned about coefficients of expansion, which is to say that different materials expand differently to variations in temperature. So, when our equipment experiences temperature changes, things are tugging and pulling on each other. I can’t say how this would effect things over time. I can say that we operate a part time service business with the goal of keeping good equipment from going into the landfill. I’ve seen gear come in that’s been in non-temperature controlled storage for 40+ years (-15 to 120+ degrees) that seemed to be okay, or just needing minor cleanup, detox, etc.

I’m leaning towards @coralkong ’s impression. Experience and real data are superior to conjecture.

Hello, When you are ready to listen make sure the equipment is acclimated to the living temperature of the house. Like 70 degrees. Once you have done that plug everything in and put in standby to let the capacitors charge up a little. After 24 hours start listening. You are preventing condensation and properly charging the system. I hope this helps.