Hi,
The reference design registers two sound cards. One for the HDMI monitor (this is the default sound card) and one for the ADAU1761. When recording or playing back audio you need to make sure that you select the correct audio device. For the ADAU1761 you also need to make sure that the internal audio routing and volume settings are configured according to your use case. The mixer settings can be changed with for example the amixer or alsamixer command line applications. You can find a description of all the controls in the ADAU1761 driver documentation. There is also an example in there on how to setup the device for playback on the headphone output.
- Lars