Treading carefully here... but how many "issues" have been raised recently about this specific topic... Especially in regards to the big K's Center Speakers? I'm beginning to redevelop my distaste for them, I'm afraid.

Perhaps we should have a sticky thread about Center Speaker Design Qualities and Performance, and how many complaints are posted about specific designs?
I agree with what's been said previously, re:
Speaker Placement
AVR Setup
Automated Room Correction programs
However, in terms of all of that, nothing will alleviate a poorly designed speaker. This is the 3rd or 4th recent post about K's Center Speaker and poor speech band performance.
@macmurchu: do please see if you can get a photo of your front setup posted as this will help us to help you in terms of speaker placement issues. Likewise, it may be beneficial to wipe and re-run any room correction you have done already, just to eliminate a poor testing by the AVR, for example. If you have not done room correction. please try it: it can always be undone... but in terms of setting distances and level, most seem to do a decent job.
Cheers!