you can´t.
the default android is sending sound over HDMI
Log.d(TAG, "active the saved audio channels " + audioOutputChannels);
// if(displayManager.getDisplayOutputType(0) == DisplayManager.DISPLAY_OUTPUT_TYPE_HDMI){
// if(!audioOutputChannels.contains(AudioManager.AUDIO_NAME_SPDIF) &&
// !audioOutputChannels.contains(AudioManager.AUDIO_NAME_HDMI)){
// audioOutputChannels.clear();
// audioOutputChannels.add(AudioManager.AUDIO_NAME_HDMI);
// }
// }else{
if(!audioOutputChannels.contains(AudioManager.AUDIO_NAME_SPDIF) &&
!audioOutputChannels.contains(AudioManager.AUDIO_NAME_CODEC)){
audioOutputChannels.clear();
audioOutputChannels.add(AudioManager.AUDIO_NAME_CODEC);
// }
}