I have 2015 XL Denali.
Got 2 headphones and 1 remote to go along with the two ceiling-mounted screens.
mmutte: My remote fits fine it the spot overhead. It is a snug fit (snaps in there), and if you do it upside down it doesn't really fit. I think the buttons face downward when done properly, though I can't recall for sure.
You can purchase extra OEM headphones through your dealer or get IR compatible ones through Amazon etc. if you want extras.