I know New Canaan has a decent music program. They are probably pretty comparable. The school systems being relatively equal, you might want to consider other deciding factors. Darien has beach and direct access to MetroNorth (no connections). New Canaan has a wonderful downtown area, Waveny park, and a town pool. I have two kids who did quite well at Saxe. They have "honors" classes at Saxe and really encourage student to excel. Average home prices are higher in New Canaan. There are less middle income properties. I've lived in both towns and know that both school systems are of the best quality. You can't go wrong with either pick. Plus,you can join the Conservatory in New Canaan whether you live there or not.
Consequently, finding the home that fits your needs can be expanded to include either town and I think you would be happy with your decision. Get a daily update from the Multiple Listing Service by logging onto http://judyhendrickson.listingbook.com.
Happy house hunting.