Tough one...I really feel for you.
I don't think it has to do his being "strong willed" - I just really think he has a very finicky tummy / appetite...just like some humans do.
Have you tried raw yet, either thawed frozen or freeze dried? Have you tried sprinkling Parmesan cheese on his food?
If you're willing to homecook - then I'd go to balanceit.com to get the diet correct.
Science Diet i/d is another one to perhaps try...
__________________ ~ A friend told me I was delusional. I nearly fell off my unicorn. ~ °¨¨¨°ºOº°¨¨¨° Ann | Pfeiffer | Marcel Verdel Purcell | Wylie | Artie °¨¨¨°ºOº°¨¨¨° |