This feels like a silly question but how do I get the Yamaha RX-V683 to use the TV connected to HDMI Out as an audio source, for when watching the TV’s tuner? I assume HDMI allows the two way transmission of audio but don’t know how to select the TV as input.
It depends upon whether or not the TV is ARC enable? ARC is shor for Audio Return Channel and is a feature whereby audio can be conveyed back from a TV vis it's ARC enabled HDMI input using the HDMI connection to an AV receiver;s or a soundbars HDMI ARC enabled output. Both devices would need br HDMI enabled though.
If your TV is ARCenabled then you'd need to connect the AV receiver's ARC enabled output to the TV's ARC enabled input. You'd nedd to turn ARC and HDMI Control (CEC) on onboard both the TV and the AV receiver.
Once setup, the TV will automatically switch the AV receiver to its associated TV/ARC source whenever you engage an audio source on the TV.