My first question: Who diagnosed him with an auditory processing disorder? This person should be advising you. Such a disorder often causes learning disabilities. Was he evaluated for this?
If your son does not have ADHD, he should not be considered for an ADHD medication. I cannot answer your questions on placement in middle school without knowing more details.
This is a cautionary tale, not just for people who have no real idea of what a learning disability is and probably suspect the whole thing is an overindulgent scam, but also for any parent of a child struggling mightily through school.
It is not common to only find an auditory processing disorder. Has your son had formal testing to clarify what other factors might contribute to his reading disability?