I have an OEM Nav unit in my '10 STA. It came factory with the 6 disc premium sound and I upgraded it to the navigation. I am satisfied with the upgrade and enjoy the other features the nav headunit provides. It is not a simple plug and play upgrade however, it involves wiring changes to the clockspring in the steering column, sync wiring in the console, steering wheel control changes, an external amp wired in, and a splitter for your XM antenna (nav antenna is already there). I did mine myself, but a good install shop will probably do it for you. You can buy kits on line with all you need, usual cost around $1500.
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