For starters, put properly rated Vibrapods under your player and pre/pro or receiver. These things are amazing for the money for cleaning up microvibrations and sound-smearing resonances.
What kind of speaker cable are you running to your center channel? And what kind of center channel spkr are you using and how is it sited/positioned?
Wide-bandwidth interconnects help, too. Without spending too much money, try a Kimber Timbre or Hero interconnect for your center channel signal chain (but do the vibration control first).