A friend of mine is going tomorrow. From both airports (Charles de Gaulle or Orly) take the train initially to 'Châtelet' Station, then take the subway train to either 'Les Sablons' or 'Pont de Neuilly' station. The street is right in between these two stations.
If you enter 'Rue de l'Hôtel de Ville' the Cathay office is about 200m to your right on the second or third floor, cannot remember.
The 'Hotel Paris Neuilly' is right at the crossing of 'Pont de Neuilly' station. Takes you about 10 minutes to walk to the Cathay office from there.
Hope this helps, good luck!