All are very good but a bit different from each other. The XT series is more 'lively' in its presentation. But they lack the layers of resolution of the C and D series. They play a bit louder (when pushed) too. Going to the C series adds a couple layers of resolution. The D adds a couple more layers over the C series. In the C and D series once you hit the 3-4 and 5 you add a dedicated midrange or 2 for even more midrange clarity. I believe in the XT series once you hit the 3 and 5 there are dedicated midrange drivers. The XT 3 has a dedicated 8" side firing bass driver where the XT 5 uses multiple 4" drivers.
The X and C series have ceramic drivers. The XT has a titanium over ceramic on the drivers which adds a bit more clarity. The D series adds a layer of diamond over the ceramic. The do that with a particle accelerator. That also adds more layers of resolution because the ceramic cone breaks up around 12Khz where the diamond breaks up just over 20Khz.
All 3 use the same tweeter
Hope that helps a bit.
The X and C series have ceramic drivers. The XT has a titanium over ceramic on the drivers which adds a bit more clarity. The D series adds a layer of diamond over the ceramic. The do that with a particle accelerator. That also adds more layers of resolution because the ceramic cone breaks up around 12Khz where the diamond breaks up just over 20Khz.
All 3 use the same tweeter
Hope that helps a bit.