The HDS-42AVR is an outboard HDMI switcher that splits the audio from the video, sending the video to the TV and the audio to the 975. There is only one connection from the HDS-42 audio out to one of the 975 inputs. Therefore, you would need to configure any of the devices being connected to the HDMI splitter to whichever HDMI port you're connecting the audio to, be it HDMI 1, 2, 3, or 4.
All of them need to be configured to the one port for both video and audio, as there is HDMI handshaking occurring.
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