The Darkglass schematic above doen't show a stereo jack - but that's what you need for sure and the blue audio out is shown to the wrong contact of the mono jack anyway, in fact the battery negative black is shown wrong also - to the jack tip.
BAD Drawing Darkglass
Hi, I have a sire jazz bass and I think the pre amp has failed, I'm thinking of going fully passive hope we could have a chat , thinking about series/parallel, please let me know if that's something you might do.