Just wondering what you found out. I didn't see your post until too late to reply, but hope you were able to find out more info. I don't know if it would help but I found that the book below has a lot of good information on juvenile arthritis in general as well as ASpA specifically; also on meds and treatments:
"It's Not Just Growing Pains: A Guide to Childhood Muscle, Bone, and Joint Pain, Rheumatic Diseases, and the Latest Treatments"
by Thomas J. A. Lehman
I got it used on the internet so you might try there. It is very easy to read and has tons of info. My son is 14 and was diagnosed at 11. His ankles were so swollen that they hit each other when he ran and he was stiff and achy. He started on NSAIDS then progressed to oral methotrexate. That wasn't enough so he was started on Enbrel about 2 years ago and then switched to Humira about 6 months ago. The Enbrel worked miracles and he was able to go back to sports full time. He started having hip, heel and ankle pain again so they switched him to Humira. It is working pretty well although he is still haveing some pain and stiffness. He loves sports and is able to do everything again, although there is pain often afterwards especially. He playing club soccer, high school soccer, and ran 7-10 miles a day with high school cross country. His doctor has put no restrictions on him and in fact loves that he is active. the only thing I would suggest is that if you have access to a pediatric rheumatologist, to use them. They definitely have a more aggressive approach to treatment than adult rheumy's. Maybe you are already using one, or possible don't have access since there are not many of them.
Let us know how it is going- good luck!