HiSunny,
I run the S-900 through a z-5500 and it's fantabulous. With the psr2100 I would use the stereox2 setting but with this s-900 I like it best through the PLII Movie setting.
The center speaker with it's own adjustable volume allows you to bring in the mid-range just as you want it. (the center speaker is lot more mid-range frequency than the front or rear speakers).
I am very happy with the combination of the two.
Jim