| What a coincidence. I just gutted out my Marcus Miller last night and installed an OBP-3. It turned out great. There is enough room in the control cavity for the 2nd 9V, but I'm only running 1 9V. I saw a picture here once of a MM bass with the battery compartment routed out for 2 9V's. It looked really professional too. I think it was a white MM bass, so if you search for that it may come up.
I actually run passive most of the time, but I wanted a better preamp in there just in case the mood strikes. What I like about the OBP-3 is that I can't hear a difference between bypass and active (set flat). The stock preamp was pretty colored, but it had an instanly good slap tone as soon as you turned it on. I'm sure that tone is in the OBP-3 somewhere, but it'll take some tweaking. I never really slap anyway.
I used the stock knobs too, except for the stacked bass/treble, where I took a stacked Fender Deluxe knob and drilled it to fit. It looks like a stock MM bass, except for the stacked knob (although it is a matching "jazz style" plastic stacked knob). I bought a full set of chrome knobs when I bought the preamp. It totally changed the look of the bass. I like the funky mismatched knobs of the MM, and now I still have it, except with a much more versatile preamp. I'll have to try and return those chrome knobs - they were just too modern looking to be putting on my bass. I really prefer the stock look. | 
