using headphones

My setup -
Raspberry Pi 3B+ IQAudio Digiamp+ Volumio 2.502

Hi all.
With the above setup, I have been trying to get sound out of either the audio jack or the audio output of the hdmi, so that I can switch from the digiamp out (speakers) and use headphones sometimes.
As far as I can see in settings/playback options I should be able to change from IQaudio device to either hdmi or phone jack. I can turn off I2S with the on/off slider.
When I do the above I still get no audio from the audio jack or the hdmi. Is there something else that I am missing?