Baking maps with ZBrush

Darkenden

I know that I can sent my model to zbrush - make some HD changes and bake displacement and normal maps. BUT - Ive already done my HD morphs and they are loaded on my daz figure. I can send it subdivided to zbrush but when I bake maps there is nothing on them because there is not any change on the figure. I want to do that because my HD details are with many sliders - I cant load it with zbrush because of the low res, but I want to make maps from them. How can I loadthe fidure without HD details, then replece it wth one with HD details and bake maps - so the maps read the diference between old model and modified model.