I'd say there will be little difference in sound between brands of DVD players when the audio is hooked up digitally. My advice, get a decent quality unit with alot of nice features. I would never pay $200.00 for an optical cable. I did pay $30.00 for a glass optical cable. Many people say they hear a difference with this cable. Many others would argue that that's impossible. At least here you're getting a glass cable that sells for less than many of the plastic ones. http://stores.ebay.com/24-7-MINIDISC...eNameZl2QQtZkm
I wouldn't be in such a hurry to upgrade your system. You could probably get sound that is a touch more open from a different brand of receiver. The difference will be slight and might not even sound good to your ears or in your room. Probably no need for a "flagship" receiver because the ORBs seem like they shouldn't be too difficult to drive. I don't know why it's so tempting to buy new stuff for your system when you're pretty satisfied with it the way it is. I do that too!!!