I think your theory is quite plausible Mick. Most aviation accidents are a combination of unlikely events and sometimes incredibly unlucky timing.
I once spoke to someone involved in the Egypt incident. The notable thing was the intensity of the fire and the very short time for the flight deck to become uninhabitable. The incident report doesn't quite convey the ferocity of it.
Have you considered the possibility of oxygen bottle explosion? It's location adjacent to the avionics rack could account for selective avionics loss.