Please read everything again.
You don't need to solder anything, each socket fits on top of another one, just like the FastATA fits in the rom sockets, so it is just to install it. The new cable is there because the old one might be to short to give a proper connection between the two boards, so it's only a cm longer than the one you already have.
-EDIT-
Links added to the last posts shows that you don't need the cable, as the one you have is already long enough. Just plug in 4 new sockets (2 in each) in the kickstart sockets, and place your FastATA on top of it.