In practice, the name 6/9 is actually an abbreviation of 6add9 because 9th chords would technically contain the 7th. They have a very particular sound due to the stacking of 4ths.

This feature is a fantastic way to learn how to build more advanced chord shapes like maj7b5. Start off by adding extra notes to a basic chord and trying to predict how its name will change. Major ...

If we follow this with a Cm7 chord for a V9 - im7 resolution, it works… but it doesn’t exactly smack us between the eyes. To get our Gaug7#9, we need to take our G9 chord and raise the 5th (D) to D# ...