I think I've just figured out the Muff tone stack

[Guitarfreak]

Didn't read it anywhere, it just kind of occurred to me whilst in the shower this morning, so bear with me if I am off base here.  After three gain stages the signal encounters a junction, one side is a high pass and the other side is a low pass and the Tone knob is acting as a blend knob setting the balance between them.

[edvard]

Bingo.
Rather like the 'tilt' control the high-end audio guys keep raving about.

[Guitarfreak]

Woo!  That's a great feeling of self-satisfaction considering I figured it out by myself.  Not that it would seem a great feat to you guys, but I'm still excited.  It seems I am getting to the point now where I 'understand' certain parts of the circuits.  Woo, indeed.  Still don't get opamps though.  Don't particularly like them so far 

[edvard]

Keep trying.
I've been avoiding op-amps lately as well, but when I was really into them, figuring out why they worked like they did opened up all sorts of trickery.
...Most of which has already been discovered and posted here by others  , but I agree that figuring it out on your own is a great feeling.
w00t!!