It's a shame they didnt put a pair of mm type pups in there. That set up sounds awesome. I would have thought what amounts to four j pickups should be pretty large sounding though. If you fitted two sets of Duncan quarter pounders you would get a huge tone but it would be expensive and there's no guarantee that you would like the tone. If it were my bass I would consider routing it for two Wilkinson mm pups. Awesome tone for very low cost. A little drastic though on such a nice bass otherwise.
Heavier strings make a big difference. Maybe try some chromes or Fender flats. I was amazed when I put some 40-100 gauge Fender flats on my P bass. Very thick and fat tone. I imagine even more so with the heavier gauge set.