A:Answer Are you using the flat screen as your speakers? if not, then it's no problem - the HDMI feed will send your VIDEO to the screen and the RECEIVER will handle all the audio (if you connect all your HDMI devices to the receiver's HDMI inputs).
Now then, if your SCREEN is being used as an "audio source" (i.e., your HDMI devices are plugged into the screen's HDMI inputs), you need to install a TOSLINK (optical) cable between the screen's Toslink output (Digital bitstream) and one of the receiver's TOSLINK digital inputs (item "5" on page 20 of the User Manual) and "assign" that input so it'll decode, etc. the audio bitstream from the screen when you select your device from the screen's remote.