STK-J2 set

[BassIsFun17]

hey everyone
i bought a used set of Basslines STK-J2's for my SX Jazz bass. My brother, who is very good with pickup installation installed them for me. The output is significantly lower than the stock SX pickups. meaning im having to turn the gain on my amp way louder to even get a usuable output; and even then it is still way lower in volume than my Suzuki P-bass with stock pickups. the p-bass has bigger strings so i assume that takes part in out put. but either way i would hope that the basslines have a higher output than the stock SX pickups. I read in searches that stacks tend to be much lower output than normal single coils. I also read that if i were to wire the pick ups in the non hum cancelling wiring that it would raise the output alot. where is a wiring diagram where i can see how to wire that? also how much more would it help? am i looking at having to get an onboard preamp if i want them to stay hum cancelling?

thanks!