I also have a 55" Samsung set attached to it. The bracket should also fit the UE55KU6400. When mounting the TV, make sure the screws are the right length!
It is very simple: Search for the VESA mount dimensions of the desired Samsung TV, e.g. on Google. Then check on the SANUS website whether these dimensions are supported by the LL11 - there you will find a table with a variety of supported VESA dimensions. Good luck!