EL34 vs. KT66 output tubes

I've had the recent opportunity to compare EL34 and KT66 output tubes in my AES sixpac monobloc amps (the amps come with the EL34's). I am surprised how much more I like the KT66's. Male vocals in particular seem to really reach out much more with the KT66's. Although bass might not be as deep as the EL34's, it has a warmer rounder feel. Is the KT66 known to be a warmer sounding tube? Does anyone have experience with both of these tubes?