Necessary changes i had to make to the default PlayerController class in the SpaceShooter demo project for Unity3d so that my Xbox 360 Big Button Controller could work (https://gist.github.com/sverrirs/0a0181fb17b29d070003)

PlayerController.cs

public void Update()
{
    bool isFiring = Input.GetButton("Fire1") || XboxBigButtonJoystick.GetButton(Controller.Red, Buttons.A);
    if (isFiring && Time.time > nextFire)
    {
        ...
    }
}

public void FixedUpdate()
{
    // Retrieve inputs
    float moveHorizontal = Input.GetAxis("Horizontal") + XboxBigButtonJoystick.GetAxis(Controller.Red, "Horizontal");
    float moveVertical = Input.GetAxis("Vertical") + XboxBigButtonJoystick.GetAxis(Controller.Red, "Vertical");

    ...
}