Well, Maximizer sets the resolution of wow automatically.

--margin w,x,y,z

means: let w pixel space between the top of the monitor (--device 0 = first monitor, --device 1 = second monitor) and the top of wow, x pixel space between the bottom of wow and the bottom of the monitor, y pixel space between the left of the monitor and the left of wow and z pixel space between the right of wow and the right of the monitor.
(damn it, i should learn better english)

so c:\Maximizer\Maximizer.exe --device 0 --margin 0,0,0,0 maximizes a instance of wow in your first monitor without any space anywhere. same with the second monitor.

(I'm really sorry for my bad englisch >.<' )

Edit: Just paste the 2 lines above into a .bat, adjust the path to maximizer, and then start it. it should start both instances of wow maximized to both monitores (notice that you have to put maximizer.exe into the directory of wow)