Does your car have the Symphony II unit, with a built-in 6-disc changer? Have you considered simply replacing it with an identical unit? Is there anything that you don't like about it, or functionality that the Alpine unit provides that you can't add to the Symphony unit?
The Symphony II unit is controlled by the instrument cluster (illumination, on/off with ignition, etc) over the CAN network. As such, there are no classic analogue triggers behind the head unit as used by most aftermarket units. That's not an unassailable problem, but it requires a bit of work to remedy. Given that the Alpine unit won't sound any better, I wouldn't bother changing unless there's a tangible need to.
Cheers,
Tom