sudo vi /etc/modules.xbian
Comment the line
#snd_bcm2835
Step 2: edit /boot/config.txt file by adding the proper overlay:
sudo vi /boot/config.txt
Make the following changes:

#dtoverlay=lirc-rpi
dtoverlay=hifiberry-digi

Step 3: Reboot.

Now you can select the Digi into the Kodi Audio Output panel.

If you use a HiFiBerry DAC/DAC+ or Amp, you need to adapt the dtoverlay line accordingly.