Hmm.. if I had placed the risers in backwards, I must have done it three times already since three risers are dead by now. And since I was neither drunk nor I am dumb ..
Strange thing tough, after the first risers died I tested all the other riser's quality attaching them to an old HD3450 like I would have done with my 7950's. All risers passed the test. Then I put back my 7950 and: boom! riser = RIP.
I assume that the 7950 draws more wattage from the molex plug than the HD3450? In combination with that the LEPA's starting current may be too high so that capacitors on the risers can't cope with it?
But if I knew that was the answer: What could I do? I really don't want to fry my risers, Cards, MoBo, BUT I also wanna Keep my LEPA