Most of the sound is in the BASS, not the guts. How does the B sound when you play the bass unamplified? Because all the pickups and pre-amp can do is translate what's happening in the wood. And I believe most of it's the neck wood. A stiffer neck will give you a "better" B string most of the time, part of the reason Sadowsky basses cost more.
But to try to improve what you have, the first thing I would do is ditch the taper-core strings. After using two sets of Stainless Lakland strings on my 55-01, I tried a set of DR Hi-Beams in the same gauges with a NON-tapered B. MUCH better response and the string sounds like the other four strings. BTW, when Bass Player Magazine did their string survey a few years ago, they found that they consistently liked non-tapered B strings better. The article commented on that, as before they did the blind test on side-by-side instruments and recorded each set of strings, they thought they liked taper-core better.
John
But to try to improve what you have, the first thing I would do is ditch the taper-core strings. After using two sets of Stainless Lakland strings on my 55-01, I tried a set of DR Hi-Beams in the same gauges with a NON-tapered B. MUCH better response and the string sounds like the other four strings. BTW, when Bass Player Magazine did their string survey a few years ago, they found that they consistently liked non-tapered B strings better. The article commented on that, as before they did the blind test on side-by-side instruments and recorded each set of strings, they thought they liked taper-core better.
John