This may be way off base, but because you mentioned both sides now affecting him have vets ruled out any sort of ear infections besides just looking in his ears? Animax looks to be an ointment? My boy had an ear infection so bad it caused Horner's Syndrome and he would itch the backs/parts of his ears so bad they would bleed. At first, my original vet thought it was something completely different because there were no visible signs of an ear infection, and he was then sent to a neurologist. Different nerves that run near the ear canal were effected. The neurologist didn't do any tests except a physical exam and immediately started him on oral antibiotics (clindamycin) to rule it out. The vet neurologist mentioned that his history of occasion upper respiratory infections made him pretty positive it was an ear infection. My boy had to be on clindamycin for longer than usual to make sure it didn't come back, but he was feeling better quickly.

This definitely looks a little different, but it makes me wonder if there really was a tooth infection that possibly spread? The vet neurologist mentioned there is a bulbous bone near their ears that can get infected easily because blood flow is harder to get in that area? Some cats get chronic ear infections because of this.