Hey Kin, yours, like mine, already has almost everything in place. If you open the door on the left side of the trunk there are 2 compartments. I think they are there for storage of small items if you did not get the CD.
I just purchased the CD changer as well and the car is already set up for it, wiring and all ! You just need to remove one of the 2 plastic boxes/compartments behind the door and you only need 1 front bracket to hold it in place from what I am told.
Just beware, I ordered mine from circle and they sent me a whole package of stuff I did not need. I now have a second identical left liner, a number or brackets, and a second identical plastic tray for the side floor area.