Played on a 7-string Romantic guitar by Mark Usherovich. I've seen a few pieces in the core repertoire that use a low D and E, indicating a 7-string was used. The Elegy by Mertz is one that comes to mind. This guitar has a very interesting design, where you can place the 7th string above the neck (as a fretted string) or off the neck (which adds some length to the string and resonance). I really love the character of Romantic guitars, but decided to use nylon strings instead of the Nylgut (