After a lot of struggles with JFETs and opamps, I finally managed to design a circuit that (at last in simulation) achieves acceptable gain control. I hope that I can compensate for the rest in software.
I ordered the PCB, but since I was going on holiday, I ordered from China this time. I've been told that my parents received some mysterious green plates, so I hope to continue as soon as I get home. Although university also starts a few days later.