How far apart are your mains ? My experience was that a center channel wasn't really needed when the mains were only a few feet apart straddling a normal sized TV, but as the system and spacing grew the center channel became more important.

It might just be that the center channel level is turned up a few dB too high.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8