I recently had a set of Bartolini Classic Bass J-style pickups wired into my Mike Lull J-style 5-string, which has an 18-volt Agular OBP-3 preamp. IMO the Bartolini pickups/Aguilar OBP-3 preamp pair up well. The OBP-3 has a lot of power to cut or boost, -although I've never found it necessary to do any drastic cutting or boosting. IMO the "flat" sound of the OBP-3 is very good to begin with.
My bass has a passive/active switch; I find the Bart's sound very Fender-ish in passive mode. In active mode, I now have sounds that I wasn't able to get from my old Duncan single coils, because of 60-cycle hum.
I've never tried a Bartolini preamp connected to J-style pickups. I do have a Roscoe 6-string with Bart soapbars and a Bart preamp. IMO the Bart preamp has a great sound, I especially like how it's high end sounds slightly compressed. But for whatever reason, it's very noisy in a few of the clubs I play at compared to my Lull with it's Aggie preamp. One of my next projects is to have my Roscoe's Bart preamp replaced with an OBP-3.