For what it is worth..
I dusted off my old laptop that I had a dual boot, Vista and WindowsXP and hooked up an old monitor to it.
Right clicked on the XP desktop selected Graphics Options > Extended Desktop.
Then started MA33jBeta and it showed on only my laptop. Went to settings Selected tab for Monitor 2 and selected Display screen saver on this desktop.. Nothing
Right click on MA3 get mini menu and selected "Windowed" instead of "Full screen" and
bingo 
MA3 is on both monitors with fish swimming from one to the other.
The selection from the main settings (space bar) Display Settings has a place to "Render same image on all monitors". That too is dependent on the "Windowed or Full Screen" selection.
Looking at the right click menu on my desktop I notice I also have a selection for "Intel Dual Display Clone", where I then have an option to select Notebook+Monitor or Monitor+Notebook. Selecting this lot and the MA3 settings section changes a bit. The Display tab no longer gives a choice about monitors. This makes sense when I think about it as both monitors are synced and act as one. MA3 will play on each (identically) and there is a performance hit as the mouse pointer flickers and the FPS drop to ~36