ok, my first reply was rather brief, so here's a more detailed answer: on my first MM2, i replaced the pickup with a Duncan ceramic pickup wired with a 3-way switch(series/parallel/single), 500k volume, and 500k tone(i just used the stock pots). the pickup sounded great, but there was a sizeable jump in volume between the series and parallel settings. and don't ask me why, but there seems to be a diffence in sound between the stock jazz bass style wiring with a volume for each coil on the OLP's, and hard-wiring it parallel to a single volume. so honestly, I'd recommend just wiring any replacement with the stock parallel wiring setup V/V/T and if you want to mess with a preamp, just use an external. i've got an Aggie 924 two band that sounds great with my current olp(which is still stock).
