Streaming from Iphone 6s - no sound from Lightning port, using adaptor

I am trying to stream Pandora from an iPhone 6s, via the Lightning port, into a DAC.

I thought it would be a pretty simple procees: Plug the Apple 3 Adaptor into the Lightning port, then a USB A into the adaptor and the USB B into the DAC.

However, when I do I still only get sound coming out of the 6S speaker(s) 

(When using the headphone and RCA's it silences the speaker, and streams to the preamp with no problem.

I am unable to find anything in Settings that directs the audio to the Lightning port, specifically.

Any help, counsel, hints, etc. would be greatly appreciated. 

Thanks, as always.