They may talk, but they don't always listen. Many advanced CEC controls are manufacturer specific, and are only guaranteed to work within the same family. That's why they all have unique names, as a marketing ploy. There's no requirement to be 100% compatible, especially with older models. However, due to customer backlash, later versions are somewhat more compatible with others.
Any CEC product will talk to another CEC product regardless of manufacturer.
CEC needs to be enabled for ARC to work. They share the same wires of the HDMI cable.
CEC has nothing to do with audio.