No real way for us to advise you on good gain settings for your particular gear. How are you doing it now?
currently iv got my amp set at the 3:00 position and the signal input from the receiver at - 4db ,an for the most part
volume is good ,loud an clear an rearly do i use the eq mode but recently over the past year its grown more harsh
an srill with an without the eq mode even while playing content that once did not sound that way ,an iv'ed even
swaped the amp with the same one that drives my fronts connecting it to that same center output from the
receiver just to make sure that the amp or receiver had no bearing on the cause of distortion nor did adjusting the
gain on the amp, just for clarification the amp used for the center was tested with my fronts from the front
connections an the amp for the fronts was used with the center connections an postion with no change
so i can safly state that the center speaker is my source of the issue
hope thats not to much of a ramble