Hi Lurk,
from our
documentation:
I²S kernel modules
You can enable I²S output by selecting one of the available items in the list. Doing so loads a pre-set collection of modules, specific for each hardware. Once set, the output interface will appear in the MPD (mpd.md) configuration menu. These modules will also auto-load on future reboots.
Navigate to the settings page MENU->Settings and select a I2S driver.
With more recent kernels (> 3.18.x ) the way to enable drivers has changed.
Frank