Would a fellow member in the 'know' please explain the difference between the standard Shaker 500 stereo and the optional Shaker 1000? According to the ordering guide, they are both 6 CD systems...with the 500 having 8 speakers and the 1000 having 10...The guide states the 1000 is in the dash. Where is the changer for the 500?? Is this option identical to the standard Mustang? Thanks...