The Klipsch speakers are extraordinarily sensitive, so it makes sense that they would need a lot less amplification.
I haven't heard the 606 bookshelf speakers, but I do have extensive experience with the B&W 603 as well as the Klipsch RP-8000F. I'm not a fan of Klipsch in general, but I do think that the RP-8000F is the better speaker here, and I think your problem is a set up issue if you were able to get equal imaging from the 603s. These speakers have very different acoustic properties, and the Klipsch will change sound more depending on how you set them up. I think that Klipsch center speaker is probably not great though.