Could be that dsp power can help to bring resonances down in piezo drivers or make the response better not only in the frequency response but also in the waterfall decay. But I did not try this.
As my use of piezos is only for the indirect sound field their frequency response is not so important.
My piezos have no damping behind the paper diaphragm and have no damping of the piezo itself by some 1mm thick rubber (Motorola piezos had some damping here.)
Maybe you could get some Monacor Piezos from Ebay directly from Germany.
The biggest difference in sound you get from covering paper diphragms with aluminium foil. I do this nearly on all my loudspeaker drivers. This is mainly due to a change in impulse response. Original drivers are poor in this discipline.
