Need help picking a better center channel speaker

withapict

OK here is what i have
Denon avr-987
Denon dvd 757
front polk rm 7400
surround polk rm 6901
center polk rm 6902
rear surround polk rm 6801
subs-
velodyne dps-12
yamaha yst-sw1500

what was the matching center for the rm 7400 mains?
or is there a suggestion to match the series speakers i have?
I bought the rm 6900 5.1 package and added the 7400's as mains and planned to get the upgraded center but 2 kids later here i am. Havnt had time to keep up lately and now im looking to complete or just continue completing my system.
Anyone have one to trade?
i have a pair of virtually new klipsch kg 5.5's
yamaha ns-333 pair
yamaha ns-c444 center
yamaha ns-777 pair
yamaha na-555 pair
yamaha htr 5590