I have NEVER, EVER brought a boxwood inside for the winter. It's unnecessary and can weaken them considerably. I've worked with Korean (the cold hardiest variety to Zone 4--a headscratcher on why anyone would bring this inside), English, American, and Japanese varieties including kingsville and other small leaved cultivars. Some bronze when they freeze (as they do in the ground in landscapes all over Va.). Their color returns without issue in the spring.
I brought my Harland boxwood inside, it has had lots of new growth in the last month. But I'm still new and have only had it since June of this year, so I'm not a good source of information.
at the nursery we protect harlandii in the winter because they are zone 7 plants. And I'm in zone 6. Though I have heard them listed as zone 8 as well, not certain. But I wouldn't think there are too many species you need to worry about at zone 9b
I brought my Harland boxwood inside, it has had lots of new growth in the last month. But I'm still new and have only had it since June of this year, so I'm not a good source of information.