Submitted my question to Crutchfield also and they recommended using a "line distribution amplifier".
https://www.crutchfield.com/I-rXYEc111/cart/EmailCart.aspx?emKey=2347928
I see that unit also on Amazon (same price) and it has good reviews. There is no balance control but I could run each...
Thank you! That appears to have pointed me in the right direction. Thinking now that I should keep the SunFire but send that output to a mixer that provides the volume and balance adjustments I am looking for to both amplifiers. Once balanced, the remote on the SunFire provides the master...
I am tuning up my music listening room and discovering that simple stereo seems to be the sound that I like best. That said, I would like to experiment with combination of speakers in the main (front) position including driving multiple pairs simultaneously.
My perfect solution would be a...