The only other things to try would be a super B complex vitamin - which will help better than just regular vitamins. When my Abby had her feather issues, I just put a lot of Brewer's yeast or Nutritional yeast in her food - maybe try that too. I hope someone smarter than me has some ideas...
One more just to show you there is hope. Here is a before and after shot of my Pekin. It's amazing what a little water, the right nutrition and some TLC will do.
Awww that looks like my poor Abby - she didn't have access to water before we got her. After a few swimming lessons and a good molt, she looks great. I also added a little ACV to her pool water for a while to help clean up her feathers (some sort of sticky residue was all over her - never did...