Have you talked to the people doing your anodizing to see if they have any suggestions.
Many years ago I tried making some parts using cast aluminum and could never get a good anodized finish. My anodizer said it was mainly due to the silicone in the casting alloy and the foundry said they had to use a high silicone alloy to have good fluidity in the melt so it would enter the mold detail.
After a couple of years I gave up and switched to machining from solid.
An open mind is a virtue...so long as all the common sense has not leaked out.