dhcp-option=3 does the trick for routing internet traffic over cell and local traffic over WiFi. Learned this long ago using the RPi with shairport-sync in my car. But keep in mind the iPhone will ignore your local DNS server if you don't hand out a gateway. I just ran into this on another project. ...

I see a lot of people asking for multiple outputs. Here is a solution:
http://www.harctoolbox.org/lirc_rpi.html

In the past I would image my 16gb card using the method detailed in this thread. But now I am using dd for windows which I sort of like better because I'm not backing up a filesystem that is active. dd for windows does stdin/stdout too so I can pipe the input/output to and from 7z. So my 1.6gb image...

I thought about doing this myself, but found this to be a easier way to get it done, and to not put the Pi under constant on/off stress. http://lifehacker.com/how-to-add-airplay-to-your-car-for-high-quality-wirele-512312902 This is the route I went a long time ago. I would buy broken APEs off eBay ...

Not to ruin your pi project, i respect em all, but would et be more easy just to buy a bluetooth module ? http://www.ebay.com/itm/351130314704?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT it was just an ideer ;) Bluetooth is lossy whereas AirPlay is lossless. AirPlay is more work but ...