Mixing two brands dry foods?
There's no problem using different brands, as log as you introduce a new food gradually. If your cat likes variety that's great. (Sometimes the advantage of staying within a brand is that you can feed different flavors (proteins) from the same line without an introductory period.)
If your cat will eat we food, it should definitely be included in his diet, for hydration purposes. As for dry food, I went though many, and have settled on Open Farm. Unfortunately my PIA won't eat wet food, so he's on Open Farm and drinking a lot of water thank goodness. I'm hoping that he will take to wet food later.
Thanks for reaching out with your question.
It's fine to feed different types of food as long as your cat is tolerating it ok e.g. no upset tummies or skin reactions. Cats have a sensitive sense of taste and as we know can be a bit fussy with foods. It might be that your cat doesn't like the new type of food and maybe it might be worth trying something else. We have a list of recommended dry foods here; 12 Best Dry Cat Foods of 2023: Unbiased Review- Cats.com
Any new foods need to be introduced over a couple of weeks by gradually increasing the amount of new food and decreasing the old food. If you notice any digestive issues or skin reactions, stop the new food. Its often easier to feed one type of dry food as you can keep the proteins and ingredients the same but if your cat prefers a mixture that's ok.
Introducing wet food is a great idea if your cat likes it. It provides a lot of moisture in their diet and keeps them hydrated. We have some recommendations here; 10 Best Healthy Canned, Soft, & Wet Cat Food 2023: Unbiased Review (cats.com)
It sounds like you're doing a great job with feeding your cat so don't worry too much, cats will eat what they want at the end of the day.
I hope that helps and reach out again if you've any more questions,