I haven't heard of the 10 string, but we've talked about harp guitars here. A 10 string is too big to barre, so you would have to have some strings tuned open and that would be more like a harp guitar. I wonder if the Glissentar by Godin might make cool slack key sounds. This fretless nylon string is at http://www.musiciansfriend.com/srs7/g=home/search/detail/base_id/128795 Jesse Tinsley