I don't think it's fair to simply call the Quatro CT just a speaker (and to compare it to other speakers). It's part of a system with many components that aren't required / included with other speakers.
Yes, it's a 3-way speaker. However, it also includes a powered sub (one in each speaker, actually), a bass management equalizer (as part of each sub) to address low-frequency room issues, and it requires bi-amping though high-pass filters before the primary amplifier (and inversely addressing that low-end rolloff with the integrated sub amps). All of these features add to the Quatro CT's greatness.
So when you listen to a set of Quatro CT's, what are you actually hearing? An excellent time and phase coherent 3-way speaker? An amplifier releaved of low-frequency reproduction duties? Stereo subs? A bass management system? Trick question. The answer is "All of the above".
I'm driving mine with just an Ayre AX-7e. All I can say is "Wow!" (and I probably only have them half broken-in).