Today, it's a good day   - I'm back in action.
What I did:

Thanks to the information by Soros Shorts and wolke, I checked the PSU-cables.
There are many differences regarding the connector-settings of ANTEC and the LEPA.
So the failure was to use the ANTEC cable-management cables with the LEPA- so i shot through the PS-ON Pin to much Power.
What happened:
1. The Raspberry PI died an heroic death, because it got more than 5V and plenty more current.
2. Like on the picture of the last post, some parts and connections of the PCB died.
So I tested again and figured out, that the connection between the socket of the PS-ON-pin was broken.
I solved this with an quick and dirty modification:
http://i59.tinypic.com/2daatki.jpg
After some more tries, I figured out that the PS did not start. So the PS-ON circuit was probably damaged.
I fixed this with an paperclip between GND and PS-ON as bypass.
The new spare Raspberry PI started again!!! (Was glad to own one!!)

After installing and connecting all together and do a test-run I was very very very lucky:
Mining again, all units working  

BUT I really think that the overheat-shutdown doesn't work regarding to the damages (I don't really care).

Thanks for your help, maybe this helps some one who made the same (facepalm) mistake like I did.