Where did you buy them? A large amount of the harder to find parts available from Chinese ebay sellers are counterfeit, they'll take whatever junk IC they have a lot of in the right package and relabel it as something more valuable. I don't see why you'd set it aside now, it sounds like you've solved the puzzle, the problem is bad DACs, and all you have to do is acquire a couple of the correct replacement parts and install them and you're done.