various gizmos are available; here's an example:
https://www.parts-express.com/parts-express-hdmi-audio-extractor-with-toslink-and-lr-audio--180-995
Otherwise, assuming your receiver is happy to deal with digital data directly -- presumably, the USB can be used,
or there should be, as implied above, a digital output (optical or coax). Of course, if it's a reasonably modern receiver, you should be able to hook the HDMI from the box directly
to it (right?).
EDIT:
If the back of your new box looks something like this:
That little port marked "S/PDIF" in the picture (which may have a little plastic plug in it) will get you the data you seek (that's a TOSLINK optical connector).
S/PDIF = "Sony/Philips Digital InterFace" (the CD audio data interchange standard)