Yes it's basically a cello with two higher strings.
I also have a metal stringed version
tuned an octave lower, this gives a full bass range + guitar range.
Cool that you are a non-pedal player and great links.
I recently build a prototype of an acoustic slide-guitar
The concept is as simple as it gets: just a box, but although it needs to be build much lighter to get a better sound response (you can land a jumbo jet on it without doing it any harm) the concept works!
As for the tuning: the six strings are tuned open C tuning and the ten strings are tuned C6, but I'm tweaking it now to a become C13 tuning (finding the
tuning is like finding the holy grail...).
Cool thing is that the ten strings can act as sympathetic strings.
The E in open C tuning can be tuned up to F, that way this tuning can be used for Indian classical music.
A great feature of a slide-guitar is that you can use just-tuning or 31-tet tuning
just (no pun intended) by retuning the strings.
And of course all time favorite Guitarix, provides a tuner which can handle al sorts of tunings...
What kind of non-pedal guitars do you have?