Thanks 75west and Flyingmouse for your responses.
I'm not sure if he is hyperfocusing as the article in the link describes how the participants becomes engulfed in the activity and loses track of time and energy. My DS was very focused on the Snap Circuits but then was quite happy to get ready and go out and play soccer for an hour (after a full day of school) - another activity which he seems to have a natural talent for and is able to concentrate on (for the most part!). Granted, he was wiped afterwards though!
I don't enough about neurofeedback to provide an opinion but it seems to be one of those methods that creates a lot of contention between experts.