Thanks.
Hold in the reset button on the AirPort Express for 9-10 seconds and then release it. Allow a full minute for it to restart to a slow, blinking amber light.
Unplug the power on the Express and temporarily move it to the same room as the AirPort Extreme for the setup.
Power up the Express and let it run a minute.
Open AirPort Utility and click on the tab at the upper left corner of the window that reads Other AirPort Base Stations (1).
Click on AirPort Express xxxxxx
Wait a minute or two while AirPort Utility analyzes the network and then announces that the Express will be configured to "Extend" your network.
Enter in a name for the AirPort Express device
Click Next
Wait a few minutes to allow AirPort Utility to read the setttings on the AirPort Extreme and configure the AirPort Express with the settings that it needs
When you see the message that Setup is Complete, click Done
Unplug the Express and move it to the desired location and power it back up. Wait a minute for a green light.
Make sure the AV receiver is powered off
Connect a known good working Ethernet cable from the LAN <-> port on the Express to the AV receiver and power up the receiver.
Check things out.