We recently posted this Instructable describing how to install a Cortado balanced-out pickup in a banjolele. This pickup runs into a little circuit that balances the signal and matches the impedance to a mixing console -- similar to a preamp or active DI. The instrument plugs straight into a mic line. (The console has to provide phantom power to the circuit.) This provides much wider bandwidth and higher signal-to-noise than you usually get from a piezo pickup.
In short, we simply removed the sound board, stuck the piezo to the head below the bridge, stuck the shielded circuit to the inside of the instrument with Velcro, stuck the mic jack to the outside, and replaced the sound board.
