I'm not familiar with the XF's yet. The girlfriend was looking at one so I've been watching the forum learning.

As for turbo and supercharging an engine it is not that uncommon. My boat is a diesel Volvo Penta with a turbo and supercharger. The supercharger works on the low to mid range, then at cruising speed the super charger turns off by an electronic clutch, and the turbo takes over. Not sure it would be easy to set up on an XF but it is not out of the realm of possibilities. I personally think it's a great combo, you get low end torque from the supercharger, then you get fuel efficiency/continued power on the top end with the turbo.