I'm using the 7.1 multi-channel input on old (one could say, very old, all pre-2010) non-HDMI AVRs - 3 from Denon, and one from Pioneer Elite. Couldn't tell you the exact model off the top of my head. Each of the 4 receivers drives 3 stereo zones, for a total of 12 zones. One streamer is connected to L/R on the MCH input, another streamer to Surround left/surround right, and finally the last one to surround back left/surround back right. Of course the speakers connected to the speaker terminals of each receivers are in different rooms. All receivers have their volume set to 0dB. Ie. I'm using each receiver as a 6-channel power amp. I don't leave them on 24/7 - I have smartplugs on them to limit power consumption.
The multi-channel inputs bypass the bass management and I believe all other digital processing in the AVRs, so this is good for connecting external DACs. I was using 12 Chromecast audios with this setup until this weekend. I'm going to switch them all to Wiim Pro Plus.
1 done so far, 11 to go.