AndroidSticks? Did you try the DroidBOX Wizard?
As mentioned, it sound as though you received an X7 which had the wrong sticker (Q7) applied to it - we had a new member of staff get the model names mixed up, sorry.
Can you test something for me please? Whilst a video is playing, but not sound comes out, can you grab a pair of headphones (any will do), and plug them into the AV socket on the back please? If sound doesn't come out, we can be fairly certain this is a configuration issue. If your headphones do play the audio you'd expect from the video, there is a remote chance the X7 has a dry joint somewhere around the HDMI socket. Our office can get quite warm with all the technology in there, which can slightly flex the circuit board. I'm grasping at straws here, but I'm struggling to imagine what else could cause this.
Ah, one moment. Can you please open this link on your X7 (using the Android browser application),
http://bit.ly/DBxcpearl and then select MX Player and "Just Once". If you get sound from your TV, we know the issue is exclusively found in XBMC.