I read once on here that it's a good idea to offer at mealtime one thing you know he'll eat, one think you think he might eat, and one thing you're pretty sure he won't eat. This way, you are setting him up for success in some way. Plus, when he sits and sees that one thing he likes on his plate, his anxiety will lessen, making meals more pleasant for everyone. All you can really do is keep offering. You are SO lucky he will eat soup....you can sneak all kinds of stuff in there...some pureed carrot or peas. My dd hates meat of any kind, but loves my chicken soup. I make the chicken soooooo tiny she can't even detect it. That way I at least know she got some protein into her!!
Pay attention to the things he likes and offer things of a similar texture. If he likes cookies, maybe try making your own oatmeal cookies...sneak some pulverized wheat-germ into them. If he likes toast, try french toast so he'll get the protien of the egg. If he'll eat cake, try banana bread made with whole whaet flour. Just brainstorming for you...I know it's tough!!