Classic speakers in new role?

Hi, new member here.

So the Apt Holman and Hafler equipment are tucked away in boxes in the basement and the Allison CD9's are joined by a pair of CD7's and a CD6 for a 5.1 surround system. My question to all you old timers out there, is (ahem) why does the 6 sound lousy as a center channel? OK, I know part of the answer - it is sitting on top of the TV, a foot and a half from the back wall, but still, it sounds way too harsh and I find myself constantly battling it by raising and lowering the volume constantly when watching movies.

Any suggestions about the settings for the center speaker - big? small? etc??? Any other suggestions?

Eric