Someone once told me that Phil Lesch (sp?) ran each string to a separate amp. They were probably just a stoned Dead head who was full of it though.
You could put separate pickups on each string and have multiple outputs. Wishbass uses 1/2 P pups sideways on EUB's. Something like that could work.
But this is in the wrong forum now.
Yes, I read this in a Grateful Dead cover. It was during the time, when they did this "Wall of sound" thing with hundreds of amps and speakers...