My daughter has not had sinus surgery or major sinus issues; but she has had periods where she just keeps getting sick; and it never ends. A couple things that have helped; Hypersal nebs via a face mask so it gets into the sinuses. SHe does not do sinus rinses, she HATES it. But the Hypersal I figure must get into her sinuses with the mask. Also, my daughter has alot of inflammation issues; I am assuming the sinus tissue can get inflamed as well from frequent bacterial infection. THis year my daughter has needed Prednisone Bursts for 5 days plus long course of oral anti's to blast away the bacteria. Don't love the idea of Prednisone but she stopped coughing in Sept after her Prednisone burst/anti treamtent. She does all her nebs via face mask to get into sinuses.
Just a few ideas; I know it is frustrating. Make sure his culture is up to date, too.