From what we can see in these spy shots, the usual nip/tuck treatment is being given to both the front and rear fascias, with revised lower air intakes making up the majority of the changes in front. The foglamps have been repositioned, the shape of the headlamp surrounds appears to be tweaked slightly, and that's about it. Around back, expect a slightly different taillamp treatment, likely with LED bulbs, but not much else.
It's possible that some enhancements have been made to the six- and eight-cylinder powertrains, but mum's the word on exactly what's happening underhood. Regardless, expect to see the refreshed X6 make its official debut in the coming months.