As far as I know, this is how it works.

It's funny you mention the MKi9200. My friend has one and I'm thinking of using it (well, the MKi9100) as my main head unit. I have a vision where most media is streamed from a phone or tablet permanently mounted in the car. The MKi series is ideal because it's able to be placed out of the way and not take up too much dash space.

For the past month, I have been using A2DP 100% of the time in my Suzuki to test how feasible it would be to rely solely on media streaming (Google Play Music, Pandora, etc). Like I said before, the sound between my CM10 Galaxy S III and JVC is just OK. Certainly acceptable in my daily driver with lots of road noise and low-end speakers.

I'm going to take things one step further this weekend and mount a Nexus 7 in the car. I will tether via Wi-Fi to my phone for now since the Nexus doesn't have a cellular radio. If it works out alright, I'm going to then see what it would take to mount the Nexus 7 in the dash. The Parrot MKi would be my new head unit in this scenario. I would link the Nexus to the Parrot over A2DP rather than Aux because I could still use my steering wheel controls. I would also have metadata on the Parrot display dependent on the app.

The Parrot is also ideal because it has an iPod interface. I have an old 160GB Classic I can leave hooked up in the glove box. It would make a good secondary audio source.