Nice bass there Rob...
I think the inclusion of a pre-amp is the best investment to be made to the tone of a kit and being much cheaper than upgrading pickups, perhaps the first option. I purchased a Belcat EQ B2T under NZ$30 including freight, and in my opinion more than makes up for any perceived shortcomings of stock PUPs.
With 3db of flat boost, and +/- 12db of boost/cut @ 85hz and 7khz, it was a real transformation to my old school (1980’s) passive Ibanez SR600, and consequently I’m installing one in my MMB 5 currently under construction. I'm configuring the humbucker for individual coil/parallel and series options, so in conjunction with the pre-amp it should cover pretty much all tone requirements.

Not too late to try one perhaps...

Cheers, Ralph

Click image for larger version. 

Name:	electronics-1.jpg 
Views:	187 
Size:	76.0 KB 
ID:	21822