One major issue is going to be condensation. Cold is OK, but not cold and damp.
Mmmm, I wouldn't subject 'nice' equipment to the rigors of a garage environment. Dust is the biggest enemy...heat and cold to the levels you've stated aren't really an issue. Moisture would be on a par with that, as Erik pointed out. If the space is subject to 'feeling damp' in the am, I'd hesitate putting those units out there...
Current shop array for me is an older Sony receiver and CD changer mated to an old SAE 2-band parametric eq. I can plug my phone with Spotify into it; local OTA radio here is pretty dismal... The Sony drives a 'low budget' line array of 3 Pioneer bookshelf pairs hung from the ceiling that are
loud enough to be heard over the machinery when desired.
If you want a 'garage stereo', I'd opt for that.. Unless you've got one of those 'pristine' spaces one sees in the adverts for tiled floors and matching tool cabinets. My shop has AC and heat, but it's not run 24/7/365. And since we work wood, dust gets EVERYWHERE despite efforts to minimize it.
Unless it'll break your heart to part with the equipment, I'd sell it off. Buy some stuff you can live with and not suffer heartbreak over if it died. Use the excess $ to add to the 'main system' or Bluetooth it so it can drive the garage set....
That's my next move, but it's not a big priority at present...
It's a garage !!! - I would never put those components in it - the dust will get everywhere and will absorb humidity = damage beyond repair.
I'd give that system a year - then it's doomed for the garbage.
But - it's your system
Personally I'd buy a mini system, like those from Yamaha - they are surprisingly good and when it dies you are only out $300
A least - buy some outdoor speakers - they are built for this type of duty