I have a 10-string guitar on order from Juan Hernandez Guitars in Valencia. I’ll upload the photos they send me of its progress. You will see that it has a lattice-braced soundboard instead of the more traditional fan bracing, with some of the lattice being cedar, the rest spruce. The soundboard is cedar. Although I haven’t yet discussed this with them, it looks like the neck will have a truss rod installed, which is not such a bad thing for a 10-string.
The guitar is their Maestro model, and is being made by Juan Hernandez himself. I’m expecting it to be a beautiful guitar!
I intend to use it in Yepes (sometimes called Modern) tuning: regular tuning for the first six strings, then a low C for the 7th string. After that the strings are exact equivalents of the 6th, 4th and 2nd frets of the 6th string, Bb, Ab, Gb. This allows all 12 notes of the chromatic scale to have as much resonance as E, B and A have on a regular 6-string.
The first picture is of a generic 65cms 10-string neck, but mine will be a special order of 664 cms, which I think will help the articulation of the lower strings. The remaining images are of my guitar.
You can click on the photos for an enlarged view: