I have a 55-02, and I won't be much help on your passive tone wiring question, but from playing in a church setting I have had the same "brittle" tone issue. I could tell as soon as I un-boxed it and played it unplugged that it was much brighter than the other basses I've played (old Fender PB 4 and a Modulus 5). First 5-6 times at church (contemporary PW w some modern gospel mixed in), I never got it dialed in, just a bad mix of bright top-end and a thin low-end (we play direct, no amps). Breakthrough for me was to set up my Helix Stomp XL for an Ampeg B-15 preamp, add some EQ for some extra low-end and mids, then on the bass roll the bass knob in active mode up 0-30% (depending on song and the overall mix) roll the treble off 20-30% and leave the mid flat. This gave me the fat bottom end that the FOH guy wants but still enough high-end for definition and have it sit up in the mix a bit. If that had not worked I was going to try flats instead of rounds, I was that desperate. But, works great now, and that Lakland low B is so sweet when you need it!