Hello,
since my upgrade to Windows 10 the second screen setting is not being recognized anymore. The whole game.prefs seems to be causing issues or something. I couldn't really change anything at the settings screen inside the game, e.g. the resolution of the primary adapter did not change and the default has been set (1024,768,60). Second adapter didn't work. After a few tries I decided to delete everything inside the folder " %LOCALAPPDATA%\Gas Powered Games\Supreme Commander Forged Alliance" and I was able again to change the game settings! But the secondary adapter still fails.
Sincere regards,
Kaishiyoku.