This is an archived documentation. It won't be updated anymore and it might not be accurate anymore.
Volumio recently has been updated to version 2. This guide is outdated.
With Volumio 1.3 the I2S settings are much easier now.
Simply select the “System” menu, select HiFiBerry (for the HiFiBerry DAC) or HiFiBerry Digi under “Activate I2S driver.” Then reboot and you’re done.