Shameless bump. I'm even interested in anyone with x000 or x100 series of any kind as I assume they will all function the same?
I have the NEX4000 in my 2006 Prius and plan on putting one into my new 2013 Prius. The answer is yes you can keep the steering wheel buttons but you will need a steering wheel adapter. The best and the one I used and recommend is: Pac-Audio.com Product Details | iPod Integration for your car and More by Pac-Audio - Connecting you to the future