To my ear, the best 2-note substitute for a dominant ninth would be the b7 and the 9 intervals, i.e. for C9, play Bb and D as a major third interval-- in dobro tuning, find it on strings 6 and 5, or strings 3 and 2....look 2 frets down (or 10 frets up) from your C major chord. For a 2 notes to repre...