If you want to use your existing pickup, the preamps for those are basically just "power boosters". It doesn't really create what's commonly known as "active" pickup system, even though it is powered. So, you're not going to get a batch of new tones beyond what an over-driven version of what you have will provide. It's still a high-impedance system.
Traditional "active" systems use low-impedance pickups and it's a different sort of preamp. They have the benefit of being essentially noiseless, but they're also not known for providing a bunch of tones so much as either a different or quieter tone. Costs more, as you have to buy a "system" as opposed to some component part to make the change.
If tonal variety is what you're looking for, you might want to look into Bill Lawrence's "
Q-Filter" device. It goes in place of the capacitor in a standard guitar/bass tone circuit, and has a couple advantages to it. One, you get a very wide variety in tone control as it basically does low and high pass filtering while a typical control is just a high-pass. Two, it doesn't require power.
I don't have any experience with them, but from what I've read they're pretty interesting devices. You can modify their behavior by adding external caps/resistors to get different curves. Since there's an inductor involved, it can actually
cut bass freqs, which most tone controls won't, so you can play games with midrange tones that most fiddles don't provide for.
