[Mihai]

You have the ability to render out alpha info together with the rgb info in the render dialog of Maxwell. Just make sure to save the output as tiff.

[Mihai]

You mean you put the image as a background in Max and then render the 3D objects over that? It's a bit of an odd way of working, how do you do color corrections and stuff like that?

There is currently no other option for Maxwell except the alpha channel, it's about as sophisticated as it is right now. There are no options for cut aways, separate shadow pass etc...