The CXS and XS use the same tweeter.......
This is what the VP of sales for Image Dynamics (Sean Adler) said about the two.......
The XS65 offers a solid midrange that increases as the spider softens and breaks in. This is good if you prefer better upper end and rely on complementary bass from your subwoofer. The XS mid driver also has a beautiful, natural roll off at approximately 1800hz (+/-).
The CXS64v.2 was designed to offer more mid-bass attack at between 80-130hz, and it does it effortlessly. However, with this mid-bass, you will lose some of your upper midrange capability. The CXS has a natural roll off starting at about 1600hz.
Both sets utilize the XS28 tweeter for a smooth response in the high range frequencies. Both crossovers offer plenty of adjustment capability for the tweeter and allow the mid driver to play through its natural roll off.
Again, if you want a bit more mid-bass, then CXS if you prefer more mid-range attack, then XS. Either way you decide, you will not be disappointed with your decision.