When I saw that the new C series models were out, I too looked for some reviews. And I too found nothing.
They look very similar, with the biggest differences being the cosmetics of the cabinets (flat top and bottom instead of curved top and bottom).
I think the newer C models use a 1" tweeter instead of a 3/4" tweeter, so that's a difference - and that might mean there are differences in the crossovers too. But overall, I would guess the speakers are far more similar than different in sound quality.