FFXIV benchmark will not crossfire. Crossfire does not work when you are at the desktop. If your game is in a window, crossfire will not work. If you are at the desktop to look at MSI afterburner, crossfire will not work. You will have have MSI afterburner track and when you leave fullscreen mode, you can look at the log to see if it was working.
Fullscreen mode is the only mode crossfire works in.