Hey Chung,
I live in Dallas in zone 8, but I think my situation can be very pertinent to you. I was taught how to over winter my deciduous trees by a club member who posts here often. What I do, is when the tree goes into dormancy and loses all it's leaves, I bring it into my garage. A deciduous tree in dormancy has no need for light, you just need to water it enough to keep the root ball from drying out. Now of course my garage may not get as cold as yours, mine will never go below 35 degrees farenheit, but you can make adjustments as well, perhaps you have a basement that will serve the purpose. You still want it to get cold/cool, but not below 25 degrees without additional protection. Your ficus needs to come inside when temps outside drop below 50 degrees farenheit. Ideal inside for your ficus would be some kind of protected area where you can control air flow, humidity, temerature, and light. A few of the members here have built some outstanding tropical indoor grow areas, if you search for them.
An example:
http://forum.bonsaitalk.com/showthr...ht=indoor+setup
Your elm should stay dormant and overwinter until your outside temperatures stay consistenly above the freezing mark. If you bring them out early, or they awake out of dormancy early, and you are forced to bring them out, a late freeze will kill any new growth, and possibly all the dormant buds on the branch as well.
If they come out of dormancy early (this happens in my zone because of the warm winters, in which I am forced to repot earlier), you need to watch your temperatures and bring them inside when it drops below freezing. Back outside when above freezing again.