I'd like to see that.

A chord like C6 in BIAB is spelled as explained above and should be giving you a major third. So, the next question is, how do you spell a maj6 chord?

Some folks think of a major 6th as a diminished seventh (not me) as contrasted to a minor 6th that they call an augmented fifth.

In some classical circles, the fifth is omitted, and the 6th is played, to indicate an inversion (example: C6 = Am). There is also some strange stuff out there, such as augmented sixth and Neapolitan sixth, but I believe as above that "major sixth" means a chord with a major triad to which the sixth is added. BIAB plays that by typing it simply with a 6, like D6.

So, we need to know what your understanding of major sixth is. Spell the chord, and we can help.

ps I love a 69 chord; used all the time in Brazilian music. There is also one of my favorites in jazz, the 13 chord. C13 includes both the sixth and minor seventh, with the sixth voiced on top as the thirteenth. But that's likely not what you want...

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