As well, the layout can be symmetric: freq/gains at the top and bottom; q and toggles at the midline of panel(or vice versa).
So, stepped Sontec isn't so far from your dreams - and no need to cut filter PCB's (nightmare IMO)... To summarize:
-Horizontal front panel layout, one channel under another
-Uraltone switches for Freq/Gain, with SMD 1206 resistors
-Lorlin etc switches for Q, 6 or 12 positions for midrange, 6 positions for low
-Gains can be wired through 7k5 or 4k7 resistors to breadboard with separated by ground cut/boost lines - saves wiring;
the cut/boost/ground lines than going right to summing (old version) or MS PCB, possible to use balanced shielded cable for this purpose.
-6/0/12db switches can be easy implemented by change of 20k summing resistors for mid bands and 10k resistor for hi shelve
(twice resistance will give 6 db range)
-Still there is place for power and M/S switches (78x5=390mm, will fit in every possible case). Possible to reserve for bands even 80mm,
it will fit in most cases with more than 415mm inside. Just mind, the weirdest case I know - Schroff Multipack with nice sides from aluminum profile-have 405mm inside.
The high band can be squeezed for some millimetres if gain/freq put in diagonal way.
The internal depth of case if switches are used way should be: about 55mm for switches + 60mm for filter boards + 140mm for ms board + some space...
Say, 280 mm will fit good and 300-320 will leave some room inside.
