I tried all ways and playing with the cable and I have another situation now: all resolutions up to ~240MHz pixelclock are stable, 1920x1200@73Hz for instance. Everything higher doesn't output anything on the FW900 though the FW900's LED turns green. Can it be it's only functioning with one HBR2 lane now? When I use a stable resolution and I move the Delock adapter at the back of the PC now and then it loses connection, not a reliable connection for sure (whether it's the Delock or GPU). Oh, and I probably can lend a HD6970 which has DP1.2. But I read online that one is also a troublemaker in combination with DP1.2. Not so interested to pay money for a newer AMD card now since the mining business made the GPU prices go sky-high. Although I would really like to return to AMD as soon as possible.