Well, diodes are variable resistors too, this time controlled by the voltage across them (see here) 
(this is what causes clipping ā once the output voltage gets high enough, typically somewhere between 0.3 and 1.0 V depending on diode type, the resistance quickly drops to near zero, and the excess voltage is shunted away)
Awesome experimentation there! Iād probably go for opamps for the later stages, though; easier to reason around, and more people here who can design for them. JFETs are more a guitar pedal thing (both by tradition and because guitar pickups have very high impedance, while synth gear tends to have low output impedance which makes it much easier to build input stages).