@tmmorris: interestingly, I used to be a musician and a bit of a sound engineer too, though less and less now. I fully agree that hard panning might be distracting, and that is why I considered having certain sources permanently limited to one side - for the sake of circuit simplicity. One could have them, attenuated, in the other channel, too, though.
OTOH a small mixer is so easy to implement (even without resorting to SMD components) that I see it as quite feasible - a quad opamp goes a long way and one can lightly accomodate several. Actually I had a vague image of, doubled for pilot and co-pilot, a stereo "power" amplifier such as TEA2225, preceeded by a summing opamp. Then add a bit if level detection, logic, programmed attenuation &c, nothing really hard.
@wigglyamp: you must be referencing the source of my vague thinking. Is there any written description of what the device actually does?