I have seperates for Home theater, I have a NAD Surround Preamp T-163 and a Musical Fidelity amp running my mains (RF-3), NAD amp running my center and an Onkyo running my surrounds. I have the mains set at large and the setting on my preamp for the center all the way up but my center is still way behind the mains, what can I do to have them at the same level