The sound bar USB is for input of photos and videos so must have an Audio input of some sort I assume. The model is HW-R430.
That´s not how this USB works. It´s a port for storage devices. The soundbar can play audio , video, foto
files from USB.
Also this USB can be used to update the firmware of it.
But it can not decode direct audio streams. HDMI to USB is not possible with it.
Which disc player is it? You can plug in optical and aux as well.
If the disc player doesn´t provide such audio ports, you can use something like this...