Personally, I find the Marantz d/a's a weak point. However, a $2000 d/a is still going to be limited by the rest of the receiver's electronics. Don't get me wrong here, I like marantz for the money. However, I don't think you can get audiophile sound out of this receiver.
The only way to be sure is to borrow a nice dvd player (500 denon or similar) and plug it into the receiver with both digital and analogue cables and switch between the 2 inputs to compare d/a's. Besides volume differences, see if highs and lows are tighter or clearer. See if the voices sound more natural?
My guess is that you will hear a difference if you spend $500 on a dvd player. Keep in mind that you may end up having to buy 6 rca cables (nice extra expense) to hook it up.
The only way to be sure is to borrow a nice dvd player (500 denon or similar) and plug it into the receiver with both digital and analogue cables and switch between the 2 inputs to compare d/a's. Besides volume differences, see if highs and lows are tighter or clearer. See if the voices sound more natural?
My guess is that you will hear a difference if you spend $500 on a dvd player. Keep in mind that you may end up having to buy 6 rca cables (nice extra expense) to hook it up.