Buddy, I dont know if I remember your original post or not about how he ended up with the Traumatic Brain Injury (TBI). Birth injury I am assuming. I also dont know quite what sort of enzyme disorder he has. He really seems like a complicated young man and he is lucky to have someone who is so dedicated to working closely to get him the help he needs but it cannot be easy.
I dont know what medications you have tried before but I have read that the AP's are on the "do not give" list. Has he ever tried any of the normal seizure medications or any of the slightly newer ones? I am thinking of things like Topamax or neurontin. Though you said he is on lyrica so I dont know that you would want to go to neurontin because that is in the same family. Topamax isnt. I am on both Topamax and neurontin and they work on different neurotransmitters.
I know there are many newer seizure medications out there and I can pull up just my insurance formulary to give you what they pay for and that wouldnt be all of them and I had noticed that there were some on there that I hadnt heard of the last time I was flipping through the pages. I dont know if that would help you at all to ask the doctors about while he is in there but if it would, I would be glad to list them for you.
Oh...and I want to say that I can agree with you on how the ritalin family of drugs does help people with Traumatic Brain Injury (TBI)'s function better. I have recently started on one and my brain is working much better.
ETA: I do take the regular anti-anxiety medications and have for a long time. I have taken ativan, klonopin and now I take xanax er. They have a klonopin melt tab. I think that was the one. You can take that one for acute emergencies. Now I really like the xanax er because I take that once a day and it just calms me for the whole day. When I was on the melt tabs...I had those and the ativan both. I took the ativan at night and the melt tabs as needed. Maybe ask the doctor about them.