I often have no sound from XBMC, but more commonly from the XBOX as a whole. This due to the fact that the optical o/p does not - allegedly - confrim to the exact standard of the SPDIF protocol. My TAG McLaren processor will find the carrier but do nothing with it. An insider has explained the above to me and suggested that a fix has been implimented for the AV192 and AV32DP but not my single processor version.
Anyway having given you that useless information, try the following.
- Toggle the input on your amp.
- Check the settings of the "audio" component for the source you are trying to playback. Press "Y" and navigate to audio and check to see if you have an active soundtrack, if not select one if you can and try again.
Other than that I am clueless sorry.