I think my next step will be to try the Fishman into some different DI/buffer amp possibilities and to cut up the Belcat and make my own carpenter jack from some old chinrest clamps, a little bit of wood, and a guitar endpin socket - and then connect it to a DI box/buffer amp. If it works I can use the other half of the Belcat to make another one!

I notice that many of the pickup systems over at that sensible place mentioned above use in effect blu-tak to attack the sensors.