I don't know if you still are considering putting your 6 silkies in the garage for the winter, or not. But I thought I would respond with a few things I have learned that might help.
I also have an attached 2-car garage to my house. When I get a new group of 10-day old chicks in early spring, I brood them out in my garage under heat lamps. I use deep bedding in the brooder, and just add fresh litter on top of the old litter as needed. There is little to no smell from my brooder, because of the size of the chicks I suppose. But also the cold temperatures in the unheated garage helps to keep down any smells. Big garage, small brooder. Not a problem for me.
I have switched to using paper shreds as my coop litter. It is practically dust free. No bad smell to clean paper shreds either compared to native smells of something like straw litter.

I don't think I would consider putting full grown chickens in my attached garage, but maybe silkies would be OK? I agree that you definitely would want to stay ahead of any bad smells, which might require more frequent cleaning inside the garage, even with a deep bedding litter system.
Anyways, smells from my chick brooder in the attached garage has never been an issue for me. If using you garage is your best option, just plan on frequent cleaning and you might be able to get through this winter with your silkies. You would be the best judge of how well it works for you.

On the other hand, you might want to ask an honest friend about any bad smells from the chickens. I think those of us keeping animals can easily go nose blind to smells of our animals that others might find offensive!