First to try to access the older 802.11g AirPort Express Base Station (AX) temporarily connect it with your computer using an Ethernet cable. Then make the required configuration changes and save them via the AirPort Utility. Finally, you can then disconnect the Ethernet cable and place the AX at the desired location.
The other thing to take into consideration. If your goal is to provide a network/Internet connection to the TV Stereo, via an Ethernet connection, the AX would need to be configured in a WDS ... and you would only be able to set up this WDS if the other router providing the Wi-Fi network is another 802.11g or 802.11n AirPort base station.