For what it's worth, I also just replaced the Infinity Reference REF-6532EX 6.5 coaxial speakers (in my rear deck - I use rear speakers) with the Kenwood Excelon KFC-X174 6.5" coaxial speakers and they are *way* better than the Infinitys as well.
Here are a few comparisons of the speakers just from a physical sense:
Fronts:
Rears:
Side:
Close-up of Kenwood:
Close-up of Infinity:
Obviously, magnet size isn't everything, but damn.... The Kenwoods make the Infinity speakers look like toys! And the difference is bass is huge as well. I'm using them in a bandpass configuration, so I'm not getting the full use of them, but they are just much "beefier" speakers.
I just like having all speakers from the same manufacturer. The X174's are the perfect companions to the component set in the front (same exact build style/materials) if you use rear speakers and they happen to be 6.5" speakers. :-)