The correct amplification of modern guitars is always a subject, but even more so, if you use a Polybass.
Guitars amps are not made for such low bass. But most bass amplifiers can handle the treble of an acoustic guitar even better than a guitar amp anyway. Try Schertler B10 for example.
Or connect to the PA directly. especially if it is a system with a subwoofer.
Distortion is altered in rather unpleasant way if the low frequency is present. So if you use a magnetic pickup as well, consider to split the guitar into two or even three way of amplification: the magnetic pickup can go to a typical electric guitar system with distortion effects while the piezo goes to the PA or an acoustic amp and some even want the Polybass effect on a separate channel to keep it dry.