Hi Jens,
I personally like Lab Gruppens myself, but I do have to disagree with you slightly ...
I was involved with an event last year where we had an event with 4 stacks of Alpha-E per side, one side driven by FP6400's, the other by Vortex 6's. It was kept like this for the whole night. We found virtually no difference in the two, the only slight bit of perceived difference was that the side with the Vortex's was slightly 'punchier'. This was the general opinion between 3 different engineers at the event. There was certainly no noticable audible difference. (Also it was a DJ so the sounds of any instruments or monitoring on stage wouldnt have had any effect)
Ok, it was hardly a fair test, the room could have played a part in it, and its hardly scientific, but on the one occasion we had a chance to AB, the 2 differenct kinds of amps seemed to behave exactly the same. (As any amps theoretically should within their operating range).
That said, give me a rack with Vortex 6's in, or give me a rack with fP6400's in and I'm a happy man.
Simon