Well the thing that I like most about two humbuckers at the same time is the natural compression you get. It makes the bass sound
compact and round like a big lead ball.
Hit the E string hard and you'll hear
BOOOOOONK.
(Instead of WHOOOOMMM or THUDD
)
You'll never get that with a single pickup.
The sweet spot is a
compromise between the warmth, the depth of the neck pickup and the agressiveness, the definition of the bridge pickup.
The sound of the two pickups together is a
combination rather than a compromise.
But you'll never get that airy and clear, yet deep, sound of a single Lo-Z in the sweet spot out of a Triumph with its two humbucking Lo-Z's. The neck pickup alone won't give you the clear tone. The bridge pickup won't give you the deep sound.
I have often thought about buying another JCS and putting two Gibson Lo-Z's in there. One at the end of the fretboard and one in the sweet spot. Combining those two would make a very warm yet tight sounding bass.