Will do. That idea made me go read more about bypass caps, too---thanks for the motivation. I knew they increased the output of a stage by reducing/eliminating negative feedback at the cathode/source/emitter, but for some reason I never put it together that that less negative feedback at the source = more input gain within the same stage, and more NFB = lower gain in that stage... cool.
you could try replacing r1 and r2 with 33k each, with a 100k trimpot between them connected to r3/c3. then you could shift the bias point of the mosfet while watching the cro to get the maximum swing from your particular device. I'm surprised this hasn't already been suggested.
"What the hell is my carpet doing to my stereo?" was scribbled in my listening notes.