Hi Danny, these are chord extensions and they are based on the degrees of the major scale.
Take a look at the E major scale: (1)E (2)F# (3)G# (4)A (5)B (6)C# (7)D# (8 or 1)E
The numbers are the degrees and the top E is 8 (the octave) or 1 of the next set going up.
A major chord is constructed with the 1, 3, and 5 degrees. The E6 and E9 chords are extended on top of the major chord (for extensions above the octave (9, 11, 13) they often build on top of the dominant 7 chord which would contains a flat 7 degree, or D in this case. If the flat 7 is not included the chord would often be called E add 9 or E add 13, etc.). So, the 6 is the C#, and the 9 is equivalent to the 2, F#, but usually an octave higher.
Your full E6 chord would be E, G#, B, C#.
Your full E9 chord would be E, G#, B, D, F#.

Hope this helps!

Michael L wrote:

Hi Danny, these are chord extensions and they are based on the degrees of the major scale.
Take a look at the E major scale: (1)E (2)F# (3)G# (4)A (5)B (6)C# (7)D# (8 or 1)E
The numbers are the degrees and the top E is 8 (the octave) or 1 of the next set going up.
A major chord is constructed with the 1, 3, and 5 degrees. The E6 and E9 chords are extended on top of the major chord (for extensions above the octave (9, 11, 13) they often build on top of the dominant 7 chord which would contains a flat 7 degree, or D in this case. If the flat 7 is not included the chord would often be called E add 9 or E add 13, etc.). So, the 6 is the C#, and the 9 is equivalent to the 2, F#, but usually an octave higher.
Your full E6 chord would be E, G#, B, C#.
Your full E9 chord would be E, G#, B, D, F#.

Hope this helps!

Very good explanation Michael

Indeed.

You also often see “6/9” chords, like so: G6/9.
That would be a major chord with a 6th and a 9th added to it: (G, B, D, E, A). This chord often appears in Western Swing / Gypsy Jazz.
It could also be minor: Gm6/9 = (G, Bb, D, E, A).

Danny, excellent question. One of my written goals is to make use of more chord voicings to help make my improvisation a little more interesting. It seems like I got stuck on triads, open chords, and barre chords for a while. Good on you for exploring this.