What is your budget? I find it odd that you want to pair up Klipsch's lower-end speakers with a receiver that costs over $1K. If you like the Klipsch sound, you may want to consider going with their Reference line. If money is a factor, you can step down to a $800 receiver such as the Dennon 2805 or the Yamaha 1500. The Reference series is more efficient than the Synergy series as well, so you will actually get more volume (and MUCH better sound!) for your dollar.
While speaker sensitivity is something to keep in mind, the most important thing when auditioning speakers is finding the ones that sound best to your ears. There are other things to consider, such as a flat frequency response, fit and finish, ect., but it all boils down to the sound.
I have a Dennon 2805 matched up with older Klipsch KG series speakers and an SC-3 center in my living room and am very happy with the receiver. I am planning on going with Klipsch or Paradigm Reference when I eventually finish the basement home theater.
I find the sound of the Dennon a bit fuller than the Yamaha. While they sound very similar to each other at lower volumes, the Yamaha sounds a bit bright to me when the volume is brought up to reference level.
