I wish I could tell you that there was a simple answer for your dog. There is not, as I am sure you have already figured out. There are a lot of things to try though.
The first thing I would do if this dog were my own would be a strict elimination diet. I am not referring to one of the diets that are sold that way by your vet or local pet superstore. Those diets are made up in factories that make up other dog foods, and accidents do happen. If you want a pure elimination diet, you have to make it up at home and everyone in the house needs to be sure that your dog is not getting any other food source. No slipping him a bite of ice cream, no food under the table, etc.
Pick one food source. You can use lamb if available. It is going to be expensive with such a big dog, and it is not going to be a balanced diet, but you can keep him on pure lamb for about 6 weeks and monitor his response. You might have to go on for 12 weeks, since you cannot really give up until then. (If you cannot afford this you can also feed brown rice with his lamb. Rice is a much better choice than some of the other grains.)
If his ears are getting better on the diet, you can start cleaning them with the dilute vinegar as described in the article. The acidic environment will make it easier for the ears to clear up.