Welcome to Audioholics GSpecialty;
What is the size of your room....? If your listening area is not really all that large, the 590 should be just fine for you....
Are you running a sub with this setup..?
I have both the 690 with my Studio's in a very very large room, and the Signature C3 (same as the CC-590) with my small room setup and they are equally as good as the other...
I bought the 690 because I wanted the best of the best with my first setup, but after getting the C3, I was equally impressed and I have no complaints. You may get a bit more midbass clarity with the 690 over the 590, but its not necessarily a huge difference, if your crossing over to a sub...
I also found a 590 on Audiogon for a good price, and I have bought a number of items from this dealer before... on Audiogon, he is a straight guy.
http://cls.audiogon.com/cgi-bin/cls.pl?spkrmoni&1214025778
You could also ask him if he has a 690, I would be very surprised if he didn't.