I like the Glockenlang preamp in my ABZ-5 a lot. It is very transparent flat, and has a nice range of EQ. The big thing on space is the battery. Sheldon provides a battery compartment in basses that have factory installed preamps, so that it doesn't need to be taking up space in the control cavity. So I would say 9 volt would be better in your case because the battery will have to be squeezed into the control cavity along with the new preamp.
Also, mine is a three band, and I have enough holes drilled for knobs. You may need to go with a 2 band to avoid drilling more holes.