There are several threads in these forums that talk about how to set nUI up on multiple monitors... just do a bit of searching to find them.
nUI6 has more robust built-in support for dealing with multiple monitors... even so far as to all placing the UI and world view on different monitors if you so desire. There is, however, no GUI at present to do that with, so you would have to hand edit the viewport info in the layout folder to set it up.
What people don't get is that I am, ultimately, an artist at heart. My brush has two colors, 1 and 0, and my canvas is made of silicon.