Heck to make it easy for you - Justin:
DACT stepped attenuator
DACT stepped attenuator or Alpha 21mm potentiometer: http://alphapotentiometers.net/html/21mm_pot_4.html
For the panel colors, i'm open to anything, but if you wanted red, for example, and nobody else wants red, I have to order a 2nd set of panels in red in case there is a flaw on one of the parts. so there would be some additional cost, probably around $200 for a one-off color.
by the way, someone should get red, i've never done it on a big amp and i think it would look cool.
black or silver will be popular so you dont have to worry about that
i sent my amp to KG to check out, he still has it and i haven't measured the output impedance. i'll see if he can check it before he ships it back