re-potting and over wintering root-bound conifers

I just re-potted several different type of conifer trees I recently purchased from local nurseries (junipers, japanese black pine, chamaecyparis, spruces etc). Some of these trees were severely rootbound but all have great potential to be bonsais because of their nebaris and aged looking thick trunks. I bought them 80% off their regular price. I re-potted them in similar size pots and used turface. Didn't cut much of the roots. I only loosened them up so new soil can go between. Anytime I repot I use turface and moss to help the re-potting process. In the past, any of my store bought trees or ones that I have collected from the wild, I've re-potted in plastic colanders for the first two years. I use turface on all my trees and they do extremely well.

My question is, for the upcoming winter months, do I put them outside or keep them in an unheated garage. I have about 80 other established bonsais and prebonsais, mainly deciduous, which I'm very familiar with. I've been working with deciduous trees for the last 35 years or so, Only during the last 5 years have I been involved with conifers. I live in Massachusetts. All of my other trees, I cover the pots with nylon mesh and bury the pot in ground. I've been doing that for years and has worked extremely well.

Any advice would be very much appreciated.

I have put new trees that were treated like you listed in a hole in the ground and also put them in my cold frame. I think the key is to keep the roots from freezing too hard because there is probably some new root growth due to the loosening of the surface and new soil. I often give them a full growing season before repotting 18 months after the initial slip pot with good soil so that I can really cut out some of the inner roots and rely on the new roots in the good soil.

Thank you. Great advice!