Later kits have the logic for the CSS, but not all of them, apparently. The short version is that one terminal on the switch goes to ground, the other to whatever pin in the Mastercell Infinitybox says to use. That's all, assuming the programming is already there. If not, you can send the boxes back for programming, or buy a programmer (as I and others have done) to re-program any of the boxes from the comfort of your own garage.
My engine harness has a starter relay in the power distribution box with two leads for the relay coil. One side is wired to ground through the clutch switch. The other will hook to the white lead coming from the rear power cell which I provides a 12 v feed to energize the vehicle starter circuit for the one button start.