I have a 455BTB with the MK-1 pickups and preamp. Some months ago, I called up Brian Ristola at Best Bass Gear and had him configure an 18 volt OBP-3 with a push/pull knob for the mids (I don't care for sweepable). It has sat on my work bench at my house since, until I recently was inspired to swap it. I decided that I should shield the control cavity while I was at it (I did the pickup cavities some time ago). I also added a few black metal knobs in ieu of using all the original Ibanez hardware parts. I did not take pictures of the swap (my apologies) but judging from my lack of photographic skill, that may not be a bad thing. So, did the sound change noticeably? Well, yes. I also put a new set of strings on the bass, so it currently has that crispy edge to it. I never found the tone of this bass inspiring but the preamp swap has certainly made it more liveable. I wouldn't go so far as to say that it is now a totally different instrument tonally, but the highs have more sheen and the lows more girth, if that makes sense. A pickup swap would likely put the icing on the cake but that would put my $$ investment in this instrument (already high) far too high.
Anyway, enclosed are a couple of pictures. The results seems to indicate that the money was well spent. YMMV.