There is a potential other way to do this, if your player comes with the tuner module.

The RioCar tuner module supports the Sony Wired Remote for controlling the RioCar via the wired remote. this would obviously be of use to you in your case if you removed all the buttons off the front of the Rio and just had a flat plate for the display. [I assume you would keep the display visible right?].

You could then mount the Sony stalk controller on your steering column out of the way of the other controls and visually not intrusive and then when the Sony head unit is in Aux [Rio Car] mode, you can use the Stalk controller to navigate tracks, menus, etc on the RioCar as required.
I know you can do this with the remote also but the Stalk interface is much more intuitive and due the different sized and shaped buttons you can do all the operations by feel and don't need to take your eyes off the road.

Maybe this isn't as nice as the integrated solution but you could do this in half a day versus half a month or more for the other alternative.
[and don't forget to factor in the time it takes for a trip to the Car audio shop to buy a new Sony head unit when your interfacing experiements accidentally fry something in the head unit - more than one person interfacing the Sony IP bus has had this experience].