My dd14 had somewhat lower CR and Writing scores on the SAT at 11 (mid 500s if I recall correctly) and her math score was a good bit lower at that point. She was a 7th grader at that age, so an 8th grader at your ds' age. I am very confident that she would do fine with college courses in most subjects, but not math yet. She's a 10th grader now.
With the ability and above level achievement scores your ds has, it is not at all surprising to me that 6th grade is not a fit. I also see no reason whatsoever that college courses would not be a fit unless they didn't work for him socially.
The few things that I'd consider in your situation would be applying to DYS (I'd really expect that he'd have no problem being accepted), and considering seeing if he can move up to 7th or even 8th grade for those subjects where he is not already going to college. Would the school be on board with a grade skip? We've found it to be a good thing for my dd who, again, isn't as advanced as your ds.
