I got this to work on my"old" white Xbox and my brand new SG3. I am the type that is good at playing around with my toys to figure stuff out but am not an expert. That being said, I can watch videos, view pics and listen to music from my phone on my Xbox. Here is how my Xbox is set up and what I did on my phone:
1.Xbox is connected to a wireless router via Ethernet power line adapters. Not sure if that matters any in regards to this issue
2.i did at first manually plug my phone into my Xbox via USB. It took a while, but the Xbox did acknowledge my phone. Again, not saying this had anything to do with my success, just sayn'.
3. On night, while looking at my pictures on my sg3 , I saw the option to "scan for nearby devices". I then noticed that instead of the option to start a sideshow, that area was replaced with an icon of a tv monitor with an arrow going into and out of it. I pressed it, looked up (my xbox main dashboard was up at the time) and the picture loaded for 3seconds and appeared!
4.it dawned on my the next night that I might be able to play music as well. Same thing. I went into the phone's default music player, hit the phone's menu, tapped scan for nearby devices, and the monitor with two arrows popped up to the left of the song title (my icon also has 1in it probably b/c I have only one compatible device).
Also worth noting, my setting-wireless network-more settings-nearby devices setting is not even turned on!
Hope this helps