It's been a long time since I've worked on Barry's 6th diminished stuff, and I've never studied it via books/dvds, only Barry's classes in NYC in the early 00s, and even then only in passing, since I went to the horn classes. My understanding of it is very fragmented and rusty, so maybe if I summarize the way I thought about it, y'all will tell me where I'm missing stuff.
- if you play any 6th chord voicing, and take it up a scale but include the diminished and natural 6th, you'll get a sound that ping pongs between diminished and whatever voicing you selected. C G A E -> D Ab B F -> E A C G -> ....
- for ii chords, use the major scale harmonized this way starting on the IV: So for a Cm7 sound, use an Eb6 voicing.
- for V chords, several options including melodic minor off the V: So for C7, you can use a Gm scale. Also could use Dbm but I'm reasonably certain Barry wouldn't have said this.
- For m7b5 chords, can use the melodic minor as if your chord is the vi: So for Em7b5, you could again use Gm
- there are of course a variety of other ways to negotiate harmony, but basically, the rule of thumb is to find a 6th voicing (can include 2 as well) that expresses the harmonic function of what you're after.
As I said, very incomplete, quite possibly some of this is wrong or not directly from Barry, but the above stuff has gotten me a surprising amount of mileage. With all this said, what am I missing and/or what do y'all recommend if I wanted to return to studying this stuff?