The pass-through function in the XBMC 12 Frodo didn’t work with ODROID. Only XBMC 13 Gotham could enable the passthrough output.
So you should use the latest Ubuntu or Debian OS image which has the XBMC 13 preinstalled.
We tested below 3 OS images.
Plug the USB-SPDIF into your board and boot.
In order to activate Passthrough Codecs, just setup PulseAudio Volume Control, as in the following.
Select Digital Output (S/PDIF) and select AC3 and DTS in the Advanced option menu.
In the XBMC, you can easily setup the passthrough function. Select the CM108 in the Audio output device and check Enable passthrough, Dolby Digital and DTS.
Note: PulseAudio does not currently allow TrueHD or DTS-MA passthrough, this is a PulseAudio limitation and not a limitation of the XBMC implementation.