Honestly it seems quite impossible that your dog is allergic to every singe protien source under the sun.
I really think you need to give more time for detox and stay away from the purina hypoallergenic foods.
Are you feeding him treats while switching foods?
Have you tried foods with only meat in them ( innova RM as an example)?
When you tried raw, was it prepakaged? If so, there are alot of additives in those, by additives I mean stuff that really doesn't need to be there.
On raw did you give broad spectrum digestive enzymes to ease the transition and help out with the digestive juices?
When you did your homecooked meals that seem to be the only thing he could eat, what was the daily meal? What did it consist of? How many protien sources were used, was there rice in the meal, or potatoes?
Have you tried duck as the only protien source in his meals? ( raw or cooked) as duck is quite low on the allergenic scale.
How often are you switching foods? How long of a time are you giving a new food before switching again.
If you are doing this too frequently this could be a main concern in the allergies. Too much of everything in his system and not enough time for one source to work.
It must really be hard to be in this situation but I really think you need to find some food with only one protien source and absolutely no grains or other stuff in it and give it a good go.
Have you tried Solid Gold Wolf King? Its made with buffalo and salmon, I'm not exactly thrilled with the food myself, but those are 2 very different protien sources that you are not going to find in many foods.
I can only question how he is managing to survive at all if there is nothing he can possibly eat?
Courage is being scared to death and saddling up anyways. ~John Wayne