Using the iPad Pro with Apple digital AV Adapter and headphone jack adapter I am using the digital AV USB-C to connect my iPad to an external display via HDMI. 
Now I want to connect external speakers via a headphone jack. 
I plugged the AV adapter into the iPad, plugged HDMI into the adapter and plugged the headphone jack in the AV adapter using the USB-C headphone jack adapter from apple. (I used the USB-C Port of the AV adapter). 

The iPad does not recognize the external speakers, and the audio is coming out of the iPad speakers. I cannot change this in the control center. 

Is the AV Adapter capable of routing audio to its USB-C port?
Or am I missing something?
The USB-C port on the Digital AV Multiport adapter is for charging only. It doesn't carry any data at all - and therefore also not sound.