Today I continued to try to taccle this problem. First I connected the monitors straight to the GTX670. Two of them with a DVI-DVI cable, the 3rd with a DVI-HDMI cable and the 4th (the separate monitor) with an active DP-DVI adapter and a DVI-DVI cable. Everything worked fine, but I couldn’t use my 4th screen and the sequence of the three monitors wasn’t correct. I could not swap them because of the length (or rather shortage) of one DVI-DVI cable.
Since I have an appointment with some people to fly in my simpit tonight, I decided to switch back to the 7770 AMD card. I have another (passive) DP converter somewhere and I will try that later. If I can get the 4th monitor to work, I will get a longer DVI-DVI cable so the GTX670 can work properly without the TH2GO DE. After installing the drivers again and several reboots I could rename the saved FSX.CFG file from the 7770 version.
After starting FSX I got black screens and nothing more. I decided to reinstall both the firmware and the drivers for the TH2GO DE. After several reboots and starting FSX again I got black screens all over the place randomly appearing and disappearing again and FSX didn’t run.
So back to the GTX670 once more, I have to be able to fly tonight, even if it is in windowed mode. I swapped the GPU’s again and connected all the screens and the TH2GO DE. When I removed the AMD drivers with DriverSweeper I realised that I hadn’t done that when I went back to the 7770. I will have to give that one a go again tomorrow. Now I can fly in windowed mode anyway, so my friends can come flying in my simpit tonight after all.