Hey Cellwelder, your math/logic is flawed.
Currently your bass has two knobs, "volume" and "tone" (or "treble control", as you called it). You will still want those on your bass when you install the preamp. So for a 3-band-preamp you will need to ADD three knobs. So in total, you would have FIVE knobs. (volume, tone, active preamp: treble/mids/bass)
Theoretically, you could replace the current, "passive treble control" with the new treble control of the active preamp, then you would have FOUR knobs in total: volume, active preamp: treble/mids/bass.
But in my experience, a passive treble control (usually called "tone" control) sounds a lot different than reducing the treble on an active preamp, so I would keep both.
Depending on the preamp you get, there are options to keep the knobs to a minimum by using "stacked knobs", but you'll need preamp that is designed/built to support that.
Then you could get away with only THREE knobs, for example: stacked knob for volume & tone, stacked knob for treble/bass, "normal" knob for mids.
There are also knobs that can additionally work like a switch, so called "push/pull knobs" (or "pots").