I know this thread is a bit old, but just wanted to chime in here:
My 'Bouchet' style guitar (built by Schramm) also seems to be very very picky about nails. If my nails are very very buffed/polished/smooth it sounds amazing. If my nails are even a little rough the trebles get thin and overly bright; particularly the 1st string gets 'pingy'.
Another thing I've noticed, not sure if it's standard for Bouchet-style guitars or not, is that due to the stiffness of the top, I really need to have good right-hand technique to get the top moving in order to get the beautiful sound. Other guitars I've played respond well to a light touch - not so this one! It's great practice to be relaxed and smooth but also firm when plucking the strings. The rewards are worth it.
I've also noticed it works well with medium-heavy tension strings. I've not tried 'low tension' strings, but both hard tension D'addarios and Hannabachs sound better than 'normal tension' of each on my particular guitar.
Note: it was built in 2005, so it's fully matured by now.
Pictures of the guitar (including bracing of the soundboard) can be found here: http://schrammguitars.com/sak.html