U1, U2, and U3 are the potentiometers.
R5, R7, R9 and R10 It's a load equivalent. This is a potentiometer in conjunction with a subsequent tone control (equalizer). The value of this resistor determines the frequency of the AFC cutoff (in conjunction with a 1 µF capacitor). And these resistors remove the constant component of the operating amplifier output voltage (together with the capacitor). That is, these are actually potentiometers (in your case).

 

Okay, thank you. Off to buy those parts.

 

I'm not sure how to find out loads. I've heard of it, but don't know what it is.

You find out the characteristics of loads by looking at the device specification or 'datasheet'. In your case the load is the OBP-3 which, according to its spec, has an input impedance of 1 MegOhm. So your splitter circuit will 'see' 1 MegOhm when driving the OBP-3.

 

Yes, I noticed just now how if the load is higher, and the resistance lower, the signal does not degrade as much. I wasn't connecting the dot's or rather the potentiometer's resistance, and the load that would connecting to it.

With all three splitters active, I will have:
3x pickups
6x500k potentiometers
2xEQ's
1xActive Mixer

But, three of those volumes (half of each splitter) are meant to nearly always go through an active mixer before going to one of the EQ's so that might help. It's a crazy build. I'm already going to have to route out the upper part of the bass for the 9v(x2) batteries, which I'm honestly not 100% certain on fitting (but I can find a place), and enlarge the control cavity to engulf the current battery cavity. I think I'll squeeze the new pickups into about a centimeter or less from becoming part of the control cavity. It's like putting a rocket engine on a pinewood derby car, and the wiring is just as crazy.

 

and the wiring is just as crazy

Make sure you use screened wire, with wires as short as possible, to minimise interference pickup.

 

Make sure you use screened wire, with wires as short as possible, to minimise interference pickup.

Will do.