thank you.
this couple of photos may help you understand my level of madness
the strings groups are as far from each other as the humbucker body allows, but the fretboard is slighter larger with some more space for the strings on both sides
actually you'll be right about phase cancellation, since i tried only one "+" wire from every coil
anyway, all that needs to understand if and how the idea of two channels works, the next step is build (or find somewhere) some small single coils for melody strings and drones
a friend on mine in germany makes his own coils for his electroacoustic hurdy gurdy, i'll do something similar, this humbucker works well enough to find how to play the dulcimer with this strings scheme and some electronics, once i figured out every ascpect of the matter i'll make the next step
regarding the under-saddle piezo, i thought somethink like what you said: cut the saddle and (somehow) put one piezo under the melody half-saddle and another under the drones, but the luthier that helped me in those "upgrades" told me that one can't cut an under-saddle piezo to a desired lenght... is that true?