The A S2000 is a different beast than your AX596, there is no comparison. Meaning The 2000 is better. There are plenty of amp/pre combinations that compete with it, but my guess is that you would be happier with the A S2000 than having any part of the AX596 involved.
Preamp Noob has a question
I have always used integrated amps in my system. Lately I've been pondering whether or not to upgrade my Yamaha AX596 to a Yamaha A-S2000 (since these are discontinued, there aren't many left). Then I started wondering if buying a used preamp and coupling it with the power amp section of my AX596 might be a better option for less money. I read some reviews on the Musical Fidelity A3cr, but apparently that preamp dates back to 2001-2002. Can you guys make some suggestions for newer, quality preamps that might be available for less than $1000? Thank you.