The EX center channels employ the same coaxial HF/MF units just as do their L/R partners and, as a result, are really good matches. OTOH, simply having any center in the center and farther from the side walls changes the timbre of its reflected sound compared with that of the L/R speakers. So a perfect match is impossible, except under extraordinary acoustical conditions, even for identical L/C/R.
Kal
Kal