Standard USB DACs don't have the authentication protocols inside them to recognize an Apple phone like that. You need a DAC made under the MFi program like the Algorhythm to do this. You could never plug an iPhone 4 into a regular USB DAC and the iPhone 5 is no exception.
Cheers...but I thought the authentication chips were in the Lightning connectors themselves (from your Lightning dissection pix)? Or I've mixed up security chips with authentication chips?
Edit: P.S. knew about the pre-Lightning. Thx for the clarification about the Lightning-supported iDevices