I would like to know, are you using a monitor/TV with built-in speakers or you have speakers connected to the audio jack in the device?
This is to perform some tests and provide you with our outcome.
I look forward to your reply.
The set up is, the HDMI cable goes to an amplifier/receiver. The receiver is connected via HDMI to a flat screen TV.
I would like you to check this Microsoft forum that is related to this.
The answer from Efraín Morales is the one I found interesting.
I look forward to your outcome with this.