Back a long time ago, some receivers had this feature.
My goal is a 7.1.4 system. I actually have three subs controlled by a MiniDSP.
I’ve got 3 external basic amps, I use one for LR front, one for center, one for a passive subwoofer. 2 channels are unused.
The MRX 720 has 11 preamp outputs and 7 amplifier outputs. However, without the feature I’m talking about, or internal routing control, it won’t let me use all 7 amps as surround amps.