Roxi,
It's good to hear that this is working for you. I have faced the same problem with my students being hesitant to be loud. I think they are becoming more comfortable with it, though. Similar to you also, I only have 4 classes. Two of my classes are 90 minutes long, though. So I actually think WBT is helping to keep the kids interested during those extended classes. In the past they have always complained about the time and I haven't heard any of those complaints this year.
I just printed off all the material for SuperSpeed 1000 and am hoping to try it in the next few weeks. I am still trying to get the class, and myself, comfortable with the basics first.