Maybe try cutting out the protein. It may not make your hair hard immediately - my hair felt great after protein treatments too, but cutting them out has been the best thing I've ever done for my hair. The awesome feeling it gave my hair didn't last and my hair always went back to being dry. Your hair may like it, but maybe it's just built up too much.
As for the deep conditioner maybe your hair is low-porosity? Do you know it's properties?