I would suggest Control 4. ( http://www.control4.com )
Get the Home Theater Controller and upgrade your Sony single disc to a DVPCX777ES and hook it up with serial and you have a really nice interface for DVD Management. The DVD only hold 400 though. If you really want to go above 400, and you can spend the money, get the Media Controller and do 2 of the DVD Changers. It's going to put you in the $3000 price range, but I don't know of a cheaper solution that does anything close. You could do it with the MX3000 and 2 DVD changers with some added software, but for a few hundred dollars more, the control 4 setup will give you a TON more. It also has A/V control and home automation control. You can build out on the system. It's pretty sweet. For what you are doing, I would look into the Control 4.
My 2 cents.