Duncan Basslines preamp - are you using it?
I just picked up a bass with a Duncan three band preamp and I'm really impressed with it. Surprised that you really don't see many basses with it installed or hear much talk about it. Maybe the slap switch is considered cheesy like the BOOM! switch on the low end Ibanez basses. Whatever the reason, I think it's now my favorite preamp. I've had Bart preamps but they seem kinda lifeless and I'd throw EMG in there too. More like sliders on an EQ pedal than tone "shaping". I have Aguilar OBP-2/3 on two basses and they're okay, but I rarely touch the knobs. Seems like the slightest tweak yields huge EQ changes. Sadowsky and Aguilar OBP-1 preamps are nice but I tend to use them like passive basses with an onboard buffer, only dialing in a little bass boost now and then.
But the Duncan preamp is really nicely voiced. I actually use all the knobs - and the slap switch - but they're all tastefully voiced to work together and the knob rotation seems like the natural amount of boost and cut you would expect from knob twiddling. I guess it seems more like amp controls on your bass, if that makes sense. I also dig the knobs that come with it. Very heavy duty and a substantial feel.
Downsides? No passive bypass, but if you know what you're doing you could probably add that.
Anyways, if you're looking for something different, give the Duncan a shot.