I'm wondering if there might be a config switch somewhere to tell it which monitor to use (1 or 2).
Good thought but AFAIK there isn’t a switch to tell Madden or most other games which monitor to use in full screen mode. The primary as assigned by the OS is all you get. You might be able to use a Hex editor to hack the game and tell it which monitor to use in full screen mode but I doubt it's worth it. But telling it where to start still wouldn’t solve the problem of using other applications on the other monitor while the game is running in full screen mode. The mouse and keyboard focus would still be locked into the game and you’d have to ALT-TAB out to use the mouse and keyboard outside the game.
Some programs allow you to set a “-window” switch at the command line or in the “Target” field of a shortcut to start it in window mode. Others have an option usually in the video settings menu to choose window or full screen. Some games require you to edit a .ini or other resource file to make it start in window mode. And some games even let you toggle between windowed and full screen modes with ALT-ENTER or another key combination. It’s a mess.
Here is a link that may offer some DIY help. http://www.realtimesoft.com/multimon/faq.asp
Madden should not crash just because your using dual monitors. It should start and run on the primary just like normal. If you haven’t already unplug one monitor and make sure it starts and runs normally. If it crashes with only one monitor hooked up then try reinstalling it and all the patches.
If it only crashes with multiple monitors then for now simplify things by taking the nVidia software out of the equation. Set it back to it’s default settings with one monitor attached and then only use the Windows Display Property tool (Right_click (on the desktop) > Properties > Settings) to configure your monitors. If the game no longer crashes with both monitors running then It’s likely nVidia and Windows weren’t playing nice with each other