Matt:
The enchilada:
http://www.steelguitarforum.com/Forum2/HTML/003549.html
Indexed:
http://steelguitarforum.com/Forum8/HTML/002238.html
Sorry I don't have the time to comment much; Trying "desperately" to hustle some Christmas for my kids; Plenty of comments in the thread though, ...addressing each item of interest you mentioned.
But the very basis of that long discussion is the "magic" relative sequence for scales, chords, fret-pocket / boxes, and substitution thinking by which we can easily navigate Steel, is:
IM7 =
IIm7 =
IIIm7b9 =
IVM7(#4) =
V7 =
VIm7b6 =
VIIm7b5b6b9 (aka half dim. or harmonic dim.) .....transposable to any root note / tonic or any other way you want to look at a transposition. Each of those chords and scale qualites all have the very same notes and so are thus located on the same 2-fret pockets / boxes on the Steel fretbaord. Pretty cool when we look at the nature of the triads therein (or a partial thereof) which is all that is required to set a root, tone or harmony in the sequence ...and even if an extension note in the pockets / bloxes are played, they CANNOT be incorrect if you're in the right pocket / box, because they're all stacked up on each box's fret in a correct harmony step sequence for each of the 7 chord and scale qualities therein.
But since we commonly use the 6th chord of the 6th tuning to orient & navigate where we're at on the 6th tuned Steel, even though every 6th chord on the neck is co-located with a Dom7 scale and not a M7 scale, such as G6's co-located scale being G7 scale's extension notes located on the F6 fret; It's thus better seen as:
I7 = IIm7b6 = IIImb5b6b9 = IVM7 = Vm7 = VIm7b9 = VIIM7(#4) ....all located on the same 2 frets pocket / box, ...again where CM7 scale would be located on the G6 and F6 frets that form the G7 pocket / box.
In any case CM7 scale notes and thus chords too, are found at the G7 scale frets pocket / box located at the G6 (and F6) chord positions. Cm7 would be up at the 3rd and 5th frets because the M7 in that box AND for the abovesaid sequence would be BbM7 = Cm7 = Dm7b6b9 = EbM7(#4) = F7 = Gm7b6 = Am7b5b6b9, ....again easier seen as F7 (Eb6) = Gm7b6 = Am7b5b6b9 = BbM7 =
Cm7 = Dm7b6b9 = EbM7(#4) = ....and again all of those scales have identical notes and are all located in the same box at the Eb6 and F6 frets. A signature minor partial chord sits in the downscale fret of every minor box chosen (Cm7 partial chord is at Eb6 while the remaining notes of Cm7 scale are at the F6 fret), while a signature Major partial chord sits on the upscale fret of a chosen Maj box (a partial of CM7 is on the G6 fret while the remaining notes of CM7 and G7 are on the F6 fret .......and in that box is CM7, Dm7, Em7b9, FM, G, Am7b6, Bm7b5b6b9 .....bringing us right back to see / know the sequence again, and that it works in all transpositions.
And that relative sequence (aka modes) is xactly why the chord change IM7 (or IIm7) > VIm7 > IIm7 (or IV) > V7 all fit so beautifully over a IM7 melody (or any root melody in the sequence since they would merely be harmonies of their root in the sequence) ...so common in old Do-Wop ...even in the song 'Sleepwalk' (with different voicing substitutions of the same relative sequence).
In the bridge of 'Sleepwalk', played in the key of C for easy visualization: When the IV Chord (F) goes to IVm (Fm) we simply move the bar up 3 frets where IVm7 / Fm7 coexists with all the other 7 RELATIVE scales of the sequence ...which is easy to analyze since that IVm chord is at the downscale end of the box making the box at Ab6 and Bb6 frets; And using the sequence easiest for our intuitive 6th chord navigation we find the chords and scales qualities in that box to be
I7 / Bb7
= IIm7b6 / Cm7b6
= IIIm7b5b6b9 / Dm7b5b6b9
= IVM7 / EbM7
= Vm7 / Fm7
= VIm7b9 / Gm7b9
= VIIM7(#4) / AM7(#4).
A nominal amount of woodshedding with a Steel and with pencil and paper will turn the barn light on pretty quick, followed pretty close by the doors swung open.
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Sorry for any typos; No time to edit much; Pretty challenging times around the "farm" here.