Trouble connecting iPhone to car stereo?

My car stereo has a USB/ipod setting and I can listen to any songs saved on the iphone by connecting from the 30 pin connetion to the UBS input. But for some reason I can't listen to radio apps like "TuneIn" or "I heart Radio". The only way I can listen to those apps is if I connect the iphone from the headphone jack to the AUX imput. How can I listen to the radio apps by connecting from the 30 pin to the USB?

I have Sony iPhone head unit. I press and hold 'Mode' which switches from controlling your playlist from the head and playing your iPhone apps including manually searching your iPod library.