OK.
I don’t have a Stage (Power Head user) but I’ve tried everything I can think of and can’t find any way to achieve what you’re looking for.
The problem with the Loop option is that even the Stereo loops are mono send/stereo return (at least on the Toaster). So when you turn on a loop you still only send one signal. Maybe the stage is different but I can’t tell for sure from the manual.
However, I’m still struggling to understand why you need two stereo outputs. What processing are you adding at the desk that differs for each signal? If it is EQ/Compression/Reverb etc. They can all be saved as part of the rig within the Kemper and sent to a single stereo pair on the desk. What am I missing?