Cambridge Audio EdgeA amp integration to Homeassistant vis RS232 and esp8266 As EdgeA as well as some of the other CambridgeAudio amps do not provide any network connectivity, I've used this as my starting point and added more functionality, including volume control https://github.com/joriskdzaack/cambridgeaudiocxa81-remote
For physical connection you will need a TTL To Rs232 male Serial DB9, please refer to attached pdf You also may be able to use with other Cambridge products, please refer to RS232 codes at https://www.cambridgeaudio.com/row/en/driver-updates