[dongioia]

Ok I got it to work by explicitly stating the same device for audio and passthrough. In my case SPDIF is on card 0 device 1:

custom audio device: plughw:0,1

custom passthrough device: plughw:0,1

This way normal audo and passthrough seems to work via the same SPDIF device without error. The only problem with this setup is that crossfading now fails with the audio init error.

So this will work only when disabling crossfading for music :/

In my case, I had to add iec98 instead of plughw:0,1 (wich is the same device, according to aplay -l).
By the way, I can hear dts and stereo sounds, but no dolby digital. XBMC gives me "failed to initialize audio settings".