What is the procedure for enabling E-ARC audio from a TV to an Anthem MRX540?

The default setting for CEC Control in the Anthem menu is off. However, if you want eARC/ARC to work, you need to turn on CEC Control in the Web UI in ‘General’ or the front panel display menu in ‘Preferences’. You also need to ensure E-ARC is switched on in the TV menu, and that the correct HDMI socket on both the TV and Anthem (HDMI out1) is used.

Sometimes, if you have another source, like an Apple TV that also has E-ARC it can throw a spanner in the works. Usually, aside from the TV and Anthem only one source should have the ARC feature switched on.