The biggest advantage the psr2000 has over the kn6500 is the mic input and harmonizer.
The kn has the advantage in hard drive option, and superb sound system. For the price - I think the 2000 is the run-a-way leader for value. If singing is not important to you, and the price doesn't matter, then the 6500 is a better keyboard. Only YOU can determine if it's $1000 better for you, though. I bought the 2000 because of the "all in one" advantage. I sing alot and the mic input is invaluable.