You have way too many amps!!
Generally speaking the simplest way to integrate a 2-channel and multi channel system is to use the two channel system for L and R at all times.
With a 2-channel preamp or integrated you look for a home-theater bypass or processor input. These special inputs bypass the volume control, letting your HT processor do all the work.
Your HT processor then sends L and R to your stereo preamp, and the remaining multi-channel signals go to another amplifier.