Upgrading the fronts on an Onkyo HTIB system

[Reckoner]

My Onkyo HTIB S780 has served me well, but I have the upgrade bug. I was thinking of upgrading the fronts with this setup:

Center: Polk CSi3
Front L/R: Polk RTi A1

Then I'll take the current fronts and move them to the rear. How big of an improvement can I expect?

 

[YOyoYOhowsDAjello]

There are new center channels to go with the RTi A series now. The CSi3 is part of the old RTi lineup. I'm not sure what kind of changes they made though to know if that's a big deal or not.