I also just purchased a new to me 2008 STi. I installed a Pioneer AVH-X3500BHS with Axxess steering wheel controls. This gave me bluetooth, ipod, pandora, hd radio and integrates to the steering wheel controls. The bluetooth still needs to be handled through the touch screen controls. I am going to try mapping some long presses of the steering wheel controls to the phone. It totaled around $400 for everything if you are handy and can install your self. I recommend a JDM/Forester dash kit so it will be a standard double din opening. Also get the harness from David at AE64.com and micro bypass to remove the limitations while driving.
I don't think there is a good way to add the features you want to the stock radio and the cost would be high. If you want nav there are several good units that would work. Replacement is the easiest path.
I don't think there is a good way to add the features you want to the stock radio and the cost would be high. If you want nav there are several good units that would work. Replacement is the easiest path.