They are out there. Hypnodrone and other builders could pull it off (he just build an active mixer for UC). I've seen a lot of schems for them out there and it doesn't look that bad.
Mostly just opamp mixing boost stages to cut the channel halving.
-Ring Mods!
"I make you chocolate"
-comesect69-via-Majin Buu-by-way-of-Dirge/mtl.asm and special consideration from CA Anderton