I would have to agree with the stereo output socket as that is what I did about 30 odd years ago on my yammy fretless bass which was the backup to my stereo Ric 4001 at the time.

It was dead simple, just replace the mono output jack, clip the capacitor off the tone pot, then make sure both pots are wired to run as volumes, then run the output signals to the different lugs on the output socket.

Only downside is this way makes it permanent stereo use however you can use it with a mono cable but that would drop one of the PUP's. Also, you can buy a stereo splitter like this one below that I bought recently for my Ric 4003. The 2 amp setup sounds awesome and easy enough to adjust their volumes so that you get a decent balance without having to fiddle around on the guitar all the time.
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