I'm not familiar with Klipsch, but I have some thoughts on this, from direct experience:
1) I personally believe that you can successfully mix speakers in a system, as long as they all faithfully target flat freq response, low phase variance (or at least similar phase variance between them), etc.
2) Even easier if they are different, but from the same manufacturer, because a lot of the components will be in common.
3) But keep in mind, that just due to your ears & head, and your room, speakers behind you, even if identical to those in front, *will* sound different. But all you're trying to do is to minimize the differences between the speakers themselves...
Bottom line, hook everything up and see (hear!

) what you think.