I'm in the same position - working with 3ds Max and Corona, struggling to convert nice Corona materials to exchange formats. My solution is to manually convert Corona materials to greatly simplified 3ds Max physical materials and export to FBX. When publishing the models, i clearly write in the description, that exchange formats have only basic materials and they will not look the same as in preview images, so the customers could have realistic expectations. It works ok for me - i have no complaints about this from the customers so far. As alternative, you can prepare your models for PBR standard - it requires more work from you, but makes the model more versatile and more valuable and usually there's no issues with conversion.