Thanks to everybody for their thoughts on this. We decided to keep the scores, based partly on the advice of our DYS family consultant and partly on the idea (hope?) that ds will probably be able to come close to matching the math score whenever he takes the SAT again -- his only prep this time around was a single practice test, on which he scored 760, so I don't think the 800 was a fluke.
I also agree with ptp's point, which I've seen made on College Confidential, that above a certain level, small differences in subtest scores just don't carry that much weight with admissions committees.
