I'm pretty sure that the last post i read from keyclone is that dual monitor support on maximizer is sill not done yet.

But if you don't want to adjust the resoloution each time you open wow you need to copy your wow folder and launch an account from each folder. This will let you change any settings you want like key settings and video settings and still have your original wow folder to save the original settings so when you want to play non- boxed you don't have to do too much setup to change back.