Hi Riaan,
I got my K400r working by using the temporary solution of not plugging the wireless receiver directly into the NUC (suggested by fellow NUC users), you may wanna consider that option till Intel fix this EMC problem. The extension don't need to be long.
I was initially using a 6" cable but has replaced it with a 4-port USB3 hub few days ago to provide more USB accessibility; now I have a total of 7 ports. Have to confess that the hub was an impulsive buy though... whahahaha.
Cheers