I have some listening materials for you! I really loved the ADDitude magazine podcasts that someone here on the boards recommended many years ago. I particularly love episode 143 for this particular topic but when I searching for them I also saw that episode 19, 89, and 141 also deal specifically with ADHD and Anxiety together. I would give them a listen if you can.

One anecdote, my DH has anxiety and ADHD. He was medicated for the ADHD as a child and hated it. He didn't really know why until I listened to that podcast. What ended up happening for him was that the ADHD meds made him much more able to concentrate on his anxieties and since those weren't being treated, it just made him really miserable. Of course, he's just one example. The podcast points out that sometimes anxiety is made better when on ADHD meds because once the distraction is improved, the things causing the anxiety stop as well!

I definitely think when dealing with two disorders you need a talented psychiatrist to help you untangle the two. It is really tricky and every kid is different. Good luck!