Interesting! I guess I shouldn't be surprised that they come with more than 3 or 4 strings!
This page has some interesting stuff on a couple of different types of six-strings: Blue Lion
and, this one has some on 6 strings, but looks like a good basic, easy to understand dulcimer place, too, so I thought, even if you don't need it, it was worth posting: Wild Dulcimer.
Sounds neat! Have fun!