I own 2 lowered cars, a VW Passat and a Z28. The correct way to lower is to purchase new springs (i.e. Eibach, H&R). They are available in numerous configurations like amt of drop and stiffness. When lowering, it's advisable to change the shocks/struts as you would need units that are correctly valved for the reduced suspension travel. If you don't the shocks will wear out prematurely.
Now, the most important thing to consider when lowering is tire wear. The negative camber associated w/ the reduction of ride height will have your tires wear on the inside. I deal w/ this on my 2 lowered cars but will not on my CX-9 (given the rplcmnt cost of 22' tires).
However, I am intrigued as to how the CX9 will handle once lowered!!!
Hope this helps.