The Klipsch will play much louder than the Elacs (especially with the 50 watts x 2 in the Onkyo). Way more efficient so if you like your music loud and or are in a big room that might pull you to them. They don't give any kind of freq. response for the Klipsch so the bass extension may be better on the Elac, By restricting the range of the bass Klipsch gets the higher efficiency spec and can play louder. That's a reasonable trade off to make in a small speaker that might be used with a subwoofer much of the time anyway.
The Elacs will be less directional having a dome tweeter instead of the horn tweeter which has been associated with Klipsch since the Jurassic. The dome will usually give you a bigger sound stage, sound better off axis...