The Kingston already has an active preamp, are you talking about dropping in new pickups? Swapping out the preamp? Do you not like the hardware that's already in there? I'm certainly not against modding, I put a set of Quarter Pounders and an Audere JZ3 in my Jazz V... Just asking the questions.
I *love* the JZ3 in my Jazz. Vol/Vol/Tone replaced by on-board 3-band EQ, master vol, pan and the Z-mode switch, but it keeps "that Jazz Bass sound." They have non-Jazz bass specific versions of the JZ, definitely worth a look if you go the on-board route.
That said, I've tried several outboard preamp options and like that route as well because you can use it with any bass. I've tried and still own several outboard preamp options, but the Aguilar Tone Hammer is my favorite. Great EQ and tone, the AGS circuit if you need dirt, DI, built like a tank, etc.
I think it comes down to what you think would work best for you. Both are good routes, both have pros & cons. Swapping out pickups AND preamp in the Kingston will probably be the more expensive route though.