wait, did you say that your sub out was your mic in? It should be the ceter channel. What you may want to do is get an active crossover that can split the sgnal before hitting the amps, that way you get your center highhs and your sub lows without sacrificing anything.
. sub/center out ~~~~~~~~~~~~~to center amp
.~~~~~~~~~~~~~~~~~~~~~~~to sub amp
You have your big amp to your two small amps? why? I'm not undestanding the reason or thought process behind it. I'm a bit slow theses days, so forgive me.