Originally Posted by line6man
Any non pcb-mount preamp can be wired with concentric pots. Any single-input preamp can be wired with an active/passive switch.
The existing mid pot most likely cannot be reused, as you will need a higher value for a passive tone control than what is currently being used for the preamp.
Z-Mode switching, to my knowledge, is simply a variable impedance loading. That can be replicated with a switch and a few resistors.
Don't know about your preamp, but my Fender Jazz preamp has pcb mount pots of values that would not be useable for a passive wiring.
Personally I like the mid control as a way to get tones that you can't get from a passive or two band setup, but that is your choice.
Note that the Z-mode thing is really designed to be used with jazz pickups and P-bass pickups have considerably different resistance and inductance. What that means is that the Z mode may not give you the tones you expect. As Line6man says, it is easy to try some different value loading resistors and see what you think.