In the mean time, I upgraded my machine to X.Org 7.0. Driver version 8174 still gives a black image.
I tried the legacy driver version 7184 and this one works perfectly. Unfortunately, 7184 is unstable on my setup. X locks up and input devices stop responding.
I really would like to get 8174 working..
I will attach two bug reports, one generated with 7184 loaded and one with 8174 loaded.
Thanks a lot for the quick response, by the way.