The aspect of the X6 which is unique is the 'Coupe' lines... The Infiniti FX is a crossover, but does not have classic coupe lines. The cars that come to mind for me when you say 'Coupe' are the Mustang Fastback and Corvette Stingray Coupe:
You can see, the FX does not have that line... Though it tried to simulate it with the chrome outline of the window profile... The overall profile is still SUV...
The new X6 most certainly has the lines of a classic Coupe:
