Preamps are made and work great. I have managed to mount them plus all the other components in a 1590B, it was a bit of a tight fit, but works!
The Plate I am using is around 80cm x 30cm and is hung on the wall in a wooden frame. I send the audio to the jack input which is connected to a small 3w amp with volume control, this outputs to the Transducer to vibrate the plate. I have 2 Piezo's on the plate which come back to the box via 2 3.5mm inputs and go to the 2 preamps. They both output to a stereo jack socket which comes back to my recording interface.
Pictures below, I will update with a video demo once I get some spare time.
Cheers