It is my understanding that breeding of protected Lucanus cervus cervus in captivity from generation to generation so far was not extremely successful, so there is still a lot to learn about their breeding specifics. One of the most restricting factors is a limited number of the specimen which can be obtained for such studies. Often, such specimen originate from one heavily inbred population, which would contribute negatively to the survival rate of the captive bred specimen. It is quite possible that using other readily available Lucanus cervus ssp as a model could be very beneficial for learning insights into the raising protected lucanus cervus cervus and restoring their population in nature.
Here are some very interesting reads about Lucanus cervus.