Have the ears been bandaged flat to the head so that even if your cat shakes his head he will not do any damage? Does he have an E-Collar to prevent self trauma?
Sometimes, even with oral medications, it may take months to get hematoma's under control. Topical ear medication is necessary, as is oral antibiotics, anti-fungals, and anti-inflammatory medication, especially, if the topicals can't be used, or they are ineffective alone.
Has your vet given your cat Prednisolone or Atopica to try to stop the cause of the aural hematoma's? If your cat continues to shake his head and scratch his ears because they hurt or they are very itchy he will continue to create hematoma's due to self trauma.
Some cats do have intractable ear problems due primarily to allergies to food and environment, ear polyps, and chronic ear mite infestation. These instigating factors cause yeast and bacterial infections in the ear. A culture and sensitivity of the ear discharge would identify the infectious causes and enable you to treat with appropriate anti-biotic or anti-fungal medications. A hypoallergenic diet may remove the food allergen from your cat's diet.
If the problem cannot be identified many end up with hematoma's that eventually become fibrosed down to cauliflower ears.
It sounds as if your vet is performing appropriate measures for the hematoma's, but if the itching or pain is severe, additional aural hematoma's will be created.
Are you using compression dressings after surgery? Sometimes the hematoma will fill back up if you don't compress the area for a while after surgery.
Hopefully, Dr. Cheng will have an answer for you. I think that ear hematomas can be difficult to treat, at least in dogs they can be.