If you’re into jazz you might want to check the videos by Jimmy Bruno at his Youtube channel. He’s one of the best jazz guitarists and educators around. Here’s his guitar site and the obligatory Myspace profile.
Imagine the tension on that guitar neck; maybe the truss bar is made of titanium. On electric guitars these extra strings are bass, e.g., F# B (followed by E A d g b e). Some accoustic eight-string guitars I believe have at least one extra treble. In the piece above as Conti plays solo, before the bassist joins in at 1:09, those deep extra basses almost sound like a regular bass guitar.
Whether Conti’s playing an eight or his regular six-stringer I’ve never seen such effortless fingering from any other guitarist.
Robert Conti is my favorite jazz guitarist (his fingers effortlessly perform every nuance of a melodic/chordal phrasing) There’s a lot of Conti videos collected at this Youtube master page
By the way, here’s Robert Conti back in the year of 1969 playing a classical guitar finger style: