Personally, I render each of my figure animations individually on a blue background. I then use After effects to color key (Blue Screen) them in. It works well, plus you can add some cool effects, like Motion blurring or ripples. Also, you can adjust the colors and bluriness of each charachter to match their position in the light. I can send you an example if you want to see it. I think you can animate poser figures in Ray Dream Studio, but you need the Patch from metacreations. Alas, Bryce does not have this option.