I can't advise you on the Klipsch, but I have listened to quite a few different Paradigm models. IMO the Monitors are well worth the extra cost. I feel the sound from the Monitor 5's vs the Phantoms is more accurate, cleaner and has greater depth. I think even the Monitor 3 is a noticably better speaker than the Phantom.
I would also highly recommend getting the Mini-Monitors or Monitor 3's instead of the Atoms for rears. The Atom does not have the same tweeter as the Monitor 5 and isn't truly timbre matched to the Monitor line. If your budget is tight, I would recommend that you put off getting the ADP side speakers in favor of upgrading the rears to Monitor 3's. That might even free up enough cash to consider upgrading the fronts to Monitor 7s. I believe you would be better off building the best 5.1 speaker system that you can afford, instead of a lesser quality 6.1 or 7.1 system. You can always add side and rear center speakers later on.
I would also highly recommend getting the Mini-Monitors or Monitor 3's instead of the Atoms for rears. The Atom does not have the same tweeter as the Monitor 5 and isn't truly timbre matched to the Monitor line. If your budget is tight, I would recommend that you put off getting the ADP side speakers in favor of upgrading the rears to Monitor 3's. That might even free up enough cash to consider upgrading the fronts to Monitor 7s. I believe you would be better off building the best 5.1 speaker system that you can afford, instead of a lesser quality 6.1 or 7.1 system. You can always add side and rear center speakers later on.