I have Infinity Kappa 6.5" components in the front and kappa 6x9s in the rear, the tweeters on the components are a little harsh, and they could use a little more mid-bass, but if I bring the bass up a little and the treble down a little, they sound great run off my Nakamichi HU with Sony amp. The 6x9s are great for rear fill. And they get REALLY loud before they distort, but I'm running ..supposedly 75w rms to each.
I haven't haven't had any reference series before, so I can't comment on those, but I like my kappas, I've had them for almost 2 years now probably and have them cranked pretty much all the time and they can take it. I have them crossed over at 50hz I think, and I can crank the bass boost to them and have never had a problem..