I spoke with Jack Woo about this amp at length at the NYC meet, there are major changes in the works for the production version. No middle knob, 4-pin jack in that space, it will use a single pot (on the left) and the large knob on the right will become the impedance switch (all good things in my book).
Also, one quick note about the design, it's a push pull transformer coupled amp and so quite different from what I was thinking it might be. Sounded pretty good too.