With the sound problem, is it with everything on the DVD player, or just some types of discs? On pages 18, 22, & 25 of the
manual, it states that it will not send audio of SACD discs via HDMI.
On page 27, you tell it which output you are using for audio when hooked up to a receiver. If that is set wrong, you will likely get no audio via HDMI. (You will need to start the process on page 26, but the issue is discussed on page 27.) You will also want to continue on to the next page, and I suggest having your DVD player NOT do any conversion, but to send each format, just as it is, to the receiver to decode.
You will also want to look at pages 81 & 82. You almost certainly have a setting wrong in the player, as your player can shut off the digital audio output.
For the Xbox, you will need to ask someone else, though I would not be surprised if it is also an improper setting in it. But I am not familiar with Xboxes. If no one else responds to this thread dealing with that within 2 days, start another thread asking about the Xbox.