Op, I had the same problem as yours. While the Tech 21 will definitely boost your signal and make it easier for you to hear, not everyone can afford it, like you.
I have a Geddy bass too and after tweaking the pickup height, string action, truss rod, and other stuff for HOURS, I finally got the sweet spot. My GL is loud and cuts through well even on a low volume...then again..I have a Rumble v3 40 which packs quite a punch even at the "2" setting on the master.
EDIT: Sometime I find my bass to be TOO loud so I adjust the pickups accordingly. I don't touch the truss rod anymore; PITA to deal with