I think I may have an answer for you.
I have several basses that are "better" than my Ibanez SR300; however, I've always loved playing the Ibanez because that neck can't be beat. The stock pickups in this bass suck!!! Let me say it again, they are terrible pieces of terd.
So I bought a set of US made Barts (that fit perfectly by the way) and had them installed by Bass Specialties in Bensalem, PA. I also had the active EQ ripped out and went passive -- I'm old school. It sounds so much better now.
The Barts you need are these:
Bartolini MK4CBC-B Dual Coil Bass pickup - Neck position http://www.catalinaguitars.com/catal...roducts_id=950
Bartolini MK4CBC-T Dual Coil Bass pickup - Bridge position http://www.catalinaguitars.com/catal...roducts_id=949