You hook your main speaker amps to the new preamp and bypass to let the AVR use its mains. All the good stuff hook it to the 2 channel side. The HT stuff to the AVR side.
If you want to bypass the other way.. Well you get to use the sucky amps in the AVR. They work BUT for HT more than stereo playback..
It really defeats the purpose of good 2 channel playback, using a 5-9 channel amp... Way to much crap in the path.. BUT they can get loud playing just two channels vs 9. I also understand you run what you can afford. Can always add a pair monoblocks or stereo amps. Bi amp?
Tubes for the top class ds for the bottom.. One up again...
Regards