Wow, ColinsMum -- Your ds sounds impressive. smile Good luck with everything...
Some thoughts -- is there a computer lab or library or some place he could go to during his "math" time to do independent work? Maybe not math work, though, if you're looking for something challenging. Maybe some sort of applied math type thing -- programming or engineering type games? And then do math at home, perhaps with a tutor? Does your ds write proofs? That might type of thing might be a nice challenge?