I'm playing a Cort NJS4 that I recently bought from a TB'er and also liking the sound the Cort pickups in this bass. I've played it at two or three shows and it's given me terrific sound with the pickup blend control typically right in the center and sometimes just a mild bump of the mid control with that knob pulled "up" (I think that position centers the mid control at 800 Hz, but not positive).I'm using a preamp made here in Portugal by a local company called MS Preamps. They were suggested by a local luthier that has started recently to work with them. This guy has used a lot of diferent preamps on his basses, according to the wishes of the clients, and he says that these are some of the best he's used so far, so I took his advice very seriously and was convinced after talking a bit with the guy behind MS Preamps.
Just to clarify, the pickups aren't Bartolini, only the original preamp. The pickups are by Cort and the model is called VTB-SB. I really like their tone.
I absolutely notice the same effect on the overall volume output of this bass with the mids boosted or cut in either the "up" or "down" position. I don't get substantial mid-scoop with the pickup blend in the middle with this bass compared with other J's I've played, but I do like to nudge the mids just a little bit to keep them present in my tone when playing both pickups full up. Mids get a bit louder, but the overall signal also gets louder.
I have an Aguilar OBP-3 that I tried in another bass a little while ago. The preamp's function was nice enough, but it didn't help the rather weak fundamental sound of the bass I tried pairing it with (Korean Lakland Skyline 44-02). Kept the preamp and found a new home for that bass. I might eventually try the Aguilar pre in this Cort, but right now I'm still getting to know the bass. It sounds quite good as is despite the mid control affecting the overall volume - I don't do significant boosting or cutting, so perhaps I don't need to fix what isn't exactly broken.
Of course I'll probably want to scratch the curiosity itch and try it a couple of months down the road...