ADD can look like CAPD. However, if you get a good psychologist/audiologist, there are tests that can differentiate between the two. I forget now, but on the CAPD testing my son had as well as on the WISC, there parts of the test that required the ability to really concentrate, which he aced. Both the psychologist and the audiologist highlighted how these parts of the tests differentiated the two.
My son has excellent focus and concentration, esp. when it's quiet. In a classroom, he can sometimes get lost when it is noisy. Our audiologist said that she thinks his auditory processing disorder will catch up and normalize to that of other kids by the time he hits puberty. I hope so! We are doing weekly piano lessons (for two years) and he will also start viola with the school orchestra next year.