You can top either EX or EX-P with Natty's. Or you can top neither. A couple of applications, allowing curing time before topping would be beneficial. IME, EX (x2) and EX-P (x3) seem to provide the most visual benefit. After allowing the final application to set-up you can then determine if you want to add a carnauba topper.
EDIT: After reading my post, my intentions were that it read IME, EX (x2) or EX-P (x3) seem to provide the most visual benefit.