Nix, nada, nothing...I only use the pickup selector.
On my Z2, I use either the front pickup or parallel.
On my AB, I installed a blend pot. Usually, it's just off center, favoring the bridge PU (where it sounds most similar to the Z2), but I'll roll it to 100% neck for mellow or slow songs.
On my amp, I turn knobs until it sounds like the wrath of God, and then I turn it up.
I'm actually thinking of pulling the pre-amps OUT of my basses, but I do like the buffering that they provide. Ideally, I'd find a couple Lane Poor 2X1AC (just buffering, no EQ) and put THOSE in the basses.
My issue is that I use onboard EQ so rarely, that when the knobs get bumped, it takes me a while to figure out what's up.
One time, my 3-year old MAXED the bass knob on my Z2 and my (rackmount) pre-amp was in the mail to the repair shop before I realized "Oh, THAT'S why I was getting so much clipping..."
Then, I had a bad run of bumping my volume knob and inadvertantly turning down. So, I switched it and the pickup selector.
My ideal setup would be just a single knob: the pickup selector.
John