Will audio gear be ok in unheated house

Maybe not the same issues, but I used a vacuum cleaner and seal-able bags, sourced from my mother in law, when we put the "stereo" in storage during our big "expedition". I'm pretty sure it got well below freezing in the unit. Everything survived with no damage I could detect. My old cabin Near Breckenridge, CO was broken into several times, BTW, but high transient population...

Don't forget salt air too as a potential issue.  This can be a bigger problem with components that don't have solder mask on the PCB's, or worse, are point to point wired.

I have had a stereo system in my barn for 10 years with no problems.   Yamaha NS 690 speakers & NAD 2400 amp.   Temps would get below freezing a couple times each winter.  And below zero the year we lost electricity.   

I would suggest burying the equipment in the ground at least 9 feet deep.  That will also help against theft.  But don't forget to mark the spot! 

They will be fine. Much to do about nothing. My speakers in my tractor barn out back (South Dakota) look and operate just fine, freezing temps in winter and lovely Black Hills summers. Like tbick I have had the same speakers in the barn for years. I heat it only when out there working in the winter with a Reznor waste oil heater. Old Sf speakers look and sound great running off an old Cyrus Integrated.