All that wire is there so I can pull out the preamp & work on it without too much hassle. To my amazement, the long wires haven't been a noise problem.
The preamp controls are (from left to right): [clean channel] Bass, Mid, Treble, Volume; clean/both/drive selector; [drive channel] Gain, 'Thick' switch (a little too close to the Gain knob!), Bass, Mid, Treble, Volume.
Here's a slightly closer view. The terminal strips are to make it easy to hook up alternate preamps. The plexiglass keeps out stray fingers (and also projectile beer cans!). I probably should have put the 'preamp in' jack on the back panel, but I was being conservative with my layout...
And now for the back. The box construction is really simple (butt joints with dowels) and I just have to unscrew a piece of quarter-round to swap chasses.
...and here's a peek at the guts of the preamp: