is becoming clearer and clearer that the negative resistance regime is how to produce massive excess energy
Negative resistance is overunity by its very definition. It just means that system generates voltage of opposite sign, when current is passing through it. One could twist the wires and bring it again to input thus increasing the current and so on...;-)
Differential negative resistance means, that voltage on circuit increases when current decreases, so that it's not necessarily connected with overunity.