Whatever sounds good in mono will sound more than twice as good in stereo. You could say that if God had intended us to listen in stereo he would have given us two ears. 🙂
Fitting a stereo pickup into your acoustic guitar is straightforward. Just fit two mono pickups in different locations. This may not be true stereo in the sense of creating a lifelike sonic image of the guitar, it will just sound better. How much better will depend on the care and attention you put into the selection of pickups and their placement.
Probably the only limitation here is that if you have a piezo pickup under the bridge, you won't be able to put another one there. (Unless you 'half and half' them – that's a possibility).
With two pickups fitted then naturally you will need a stereo preamp. That's where a device such as the Pendulum SPS-1 Stereo Preamp comes in.
The Pendulum SPS-1 is a rack mounting unit that requires an additional 'pickup preamp module' – slightly confusing terminology, but basically you need a preamp module physically close to the guitar, which connects via a cable to the rack mounting box.
Pendulum offer two alternatives. The pickup/pickup model can handle the outputs of two pickups fitted inside the guitar. The pickup/mic model is for one pickup and one internal microphone. A microphone, even an internal one, tends to pick up more of the acoustic character of the instrument than a contact pickup that is sensitive only to vibrations in the solid material of the guitar.
Both preamp modules have a balance control that allows you to favor one pickup over the other, or the pickup over the mic or vice versa. Also there is an overall volume control that is handy for operation on stage.
The SPS-1 itself is very versatile. Its two channels can take the signals from the preamp module, or you can connect conventional mics or line level sources. So you can use it as a conventional stereo mic preamplifier if you wish, with 48 volt phantom power if needed.
Either way you use it, there is a three-band parametric EQ on each channel with channel insert points for additional effects processing.
For the gigging acoustic guitar player, the Pendulum SPS-1 makes a powerful and easy to use package. For a band that incorporates acoustic guitar, suddenly there is a lot more fun to be had for the guitar tech. Hopefully audiences too will appreciate the difference.