That's ok about the pics

, I know alot of people wall mount and have cabinets.
Ok, first let's check this. Does either the TV or Xbox have an digital audio out connected to your AVR? (they would be optical connections)
If it's no, you'll have to put a connection in and the easiest way would be to just connect the xbox to the AVR.
If it's yes, look to see which input on the AVR it's plugged into (it should be either the CD recorder or Satellite input), make sure it's connected to an input and not an output, then select that input and see if you get sound. If it works, make sure you're remote selects that input on your AVR if you can. I haven't used the harmony before and I don't know if it lets you stack multiple commands for a certain action (like switching your TV input to xbox and then switching your AVR to the correct input). If it doesn't let you, then just assign one button to switch the TV and another to switch the AVR.
If you don't get any sound, you may have a bad input so try the other port and see if that works.
If it's still no, now it's getting tricky for me. Could be a bad cable, but perhaps the on the TV/xbox there might be a setting that you need to turn on or something like that to get it to output on the optical. I can't find an online manual for the xbox for me to check so I can't help there so you'll have to poke around in the settings and see if there is anything there (I think it's always on but looking around doesn't hurt). If the TV is connected, make sure that the external speaker is set to on and look for anything else that might have something to do with it (the Samsung manual isn't the best at telling you what's going on).