I need help wiring a Xantech 291 hidden link

Hi,
This might sound like a stupid question but I know almost nothing about wires.
I just bought a 291Kit hidden link which I intend to use to control my AV equipement in my basic multi-room installation.
I have seen on Xantech site that to expand it for multi-room, you have to cut the connector and and plug the wires to the IR wires that make the connection between the room. Now my question is the following. The Xantech device has 3 wires: a black for ground, a red for current and a white for data. on the other hand, the cable I have in my walls (which I bought from and AV specialist store) has 4 branches: 1 red, 1 white and 2 blacks. How should I connect those 2 wires together? What should I do with the extra black branch?
thank you very much for your help