Will audio gear be ok in unheated house

Rather than using garbage bags, use moving size cling wrap to wrap your gear. It can be purchased on Amazon or at Home Depot. The 20" wide rolls work well for audio components and speakers. I use it to store my audio equipment that is not currently being used. I wrap two or three turns length wise and width wise and it forms a good tight seal that will keep out insects and moisture from anything short of full on flood submergence. I also use it for extra shipping protection when I sell gear.  

Beginning to sound like it's just easier to take your speakers with you!

Peace of mind knowing they're safe.

In the long run, leaving your stereo equipment in an unheated home where the outside temperature drops below freezing and/or below 50 degrees where dampness exists, is not a good idea, and eventually will damage your equipment.

Fwiw, I've left my porch system (Integra receiver and disc changer) outside in a cabinet through ten Chicago winters and it still works fine. Now, I wouldn't be so cavalier with high-end gear, and I don't recommend it for others, but there you go.

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.