Srt 8 factory kicker system

I have installed a zx mono amp for a solo baric sub, and a zx 4 channel amp for the rest of my speakers, but the factory head unit which powers off of the factory 8 channel amp which is made by kicker only allows highs or mids to sound through the rest of my speakers.  It will not allow both.  I was told it was the digital signal from the factory amp.  I wanted it out, but the head unit needs it to run certain features.  What is the problem here or what other options do I have?