The ideal molar ratio of adipic acid to hexamethylenediamine for the synthesis of nylon-6,6 with the highest possible yield and quality is 1:1. This is because one molecule of adipic acid reacts with one molecule of hexamethylenediamine to form one molecule of nylon-6,6 and two molecules of water. Maintaining a 1:1 molar ratio ensures that both reactants are fully consumed, minimizing waste and maximizing the yield of the desired product.