After much research I got the Arc to work perfectly. I located a website that explained how modern tv’s store the CEC information and the issue of this being not updated when you add a new device. In my case with my Sony android tv, the amp was connecting but the tv was not recognising the device to output the arc info. I had to disconnect all hdmi cables from the tv except the one attached to hdmi3 arc port. I then had to power off the tv and switch off the power at the socket. This clears the tv CEC resident data. I then powered up the amp, switched on the tv. The tv instantly started outputting an audio signal on the arc output. This was shown by the amp showing DD+ this had previously never activated. . I then plugged back into the tv the Blu-ray player and Firetv and all works correctly. So I’m summary nothing is connected differently but it was the order of connection and the requirement to clear the tv CEC info that was key. According to my research this is a very very common issue if you want to add arc functionality to equipment that has already been connected and set up.
