I have 2 monitors of the same spec and resolution, 3840 x 2160 max at 60Hz, and normally run Trainz on the LH screen in windowed but full screen, and CM on the RH screen. I only use a resolution of 2480 x 1080 to run Trainz to keep the video card load down. If you minimize the window you can then drag and resize the view across onto the 2nd screen so that it fills both screens if that is your want. For this to look reasonable you need monitors with minimum width, or no frames, to have a good picture.
This is the one monitor shot at 2048 x 1080:
This is with the picture stretched over two monitors so the equivalent of 4096 x 1080. This is just a screenshot so the monitor frames do not show but a thin grey line in the middle defines the two screens:
All of this is handled by the video card and not
TRAINZ. I originally dragged the Trainz Launcher dialog box to the RH screen and this position is remembered by the program so it always opens in the same position. Then, when you initially open any of the CM boxes you just need to drag them to the same screen and they will also open in the same location next time.
For 3 screens you can run any variation you like and they should all work.
NOTE: DO NOT tick
Full Screen in the
General Tab of
Trainz Settings as this locks the picture to the screen size and you cannot manipulate it.