I'm sorry to hear about your son's eating difficulties. My 9-year old son also had (and still has) many food aversions. He had difficulties with the odor, texture, and temperature of foods, and would only eat about 10 or 12 foods period. He still refuses to eat fruits and vegetables, and refuses to drink milk, but we are making progress.
I have found that the book "Just Take a Bite: Easy, Effective Answers to Food Aversions and Eating Challenges!" by Lori Ernsperger and Tania Stegen-Hanson is an excellent resource book. One is an autism and behavioral consultant, and the other is a pediatric occupational therapist. The book talks about "resistant" vs. "picky" eaters, oral-motor development, environmental and behavioral factors contributing to problems with eating, sensory and motor-based problems affecting the resistant eater, designing and implementing a comprehensive treatment plan, environmental controls (i.e. mealtime schedule and setting, portion size, food selection, etc.), and the stages of sensory development for eating (acceptance, touch, smell, taste, and eating new foods). This book has a variety of clear and practical lessons and goals for assisting children with mealtime struggles. Some of the lessons include creating games for touching, smelling, and even painting with food to encourage the physical enjoyment of eating. This book would be a great place for you to start. And, consulting with a pediatric occupational therapist in your area might help too.
Hang in there. Modifying your son's eating habits and food aversions can be a long and difficult road. But, you are obviously a mom who doesn't give up! Keep doing your research, and hopefully your son will make some progress!
C.