some very interesting things you are planning .
hopefully you get your parts soon , im very interested in the breakout box.
Only one cable leading off the WD is such a clean solution.
plus the switchable A/B TRS jack ( "normally closed" between A and B)
mounted where my "B" jack is
"A" is ring , "B" is tip , ... "C" is a mono jack
this frees the "A" position for an Expression jack ,
thats to the left side if you flip the WD . (hihat and stuff).
btw : sounds no 58 and 59 change when you press EXP ... try it out
thats the fun ... to discover all the possibilitiesAnd it needs experimentation.