So it appears that OpenELEC, as of now, cannot handle 7.1 AAC files (compressed from DTS MA tracks). What I get, consistently, is silence. I'm not sure if this is something the Pi can't handle, something the XBMC can't handle, an MPEG-LA licensing issue, or an encoding issue. All references to 7.1 AAC and XBMC I've found have to do with wrong channel maps with the Windows version. I suspect that it might be a licensing or encoding issue because other 'embedded' products (PS3, iPad Mini) also apparently have issues...but I'm really not sure. I asked this question already at the RPi section of the OpenELEC forums and got no response.