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I thought it would be input resistors, but it seems there's capacitance to be added too.
From the manual:

Input loading
The standard settings on the 8000PPA will suit the majority of modern cartridges, but may be fine-tuned if required. Follow the instructions supplied with your cartridge for guidance.

Making up load plugs
Use the instructions below to calculate the value of the load resistor and capacitor. Solder the components to a phono plug, connecting one lead of each component to the signal pin and the other lead to the metal body. Make two identical plugs and insert one into each load socket. If you are uncertain consult your dealer for assistance.

Calculating the resistor value 
Determine the recommended load from the cartridge instructions.
Calculate the load resistance using the formula:
^R LOAD = (^RPPA – ^RTERM) / ^RPPA x ^RTERM
^RLOAD is the load resistor that you need in the plug.
^RTERM is the load resistance in Ohms that the cartridge needs.
^RPPA is the factory fitted input resistance of the 8000PPA 47kOhms when set to MM and 470 Ohms when set to MC

Calculating the capacitor value
Calculate the load capacitor using the following formula:
^CLOAD = ^CTERM – ^CLEAD – ^CPPA
^CLOAD is the load capacitor (in pF) you need in the plug.
^CTERM is the capacitance (in pF) that the cartridge needs.
^CLEAD is the capacitance of the leads between the cartridge and the 8000PPA (tonearm lead capacitance) in pF.
^CPPA is the factory fitted input capacitance of the 8000PPA – 100 pF when set to MM and 3300 pF when set to MC.
Switch the 8000PPA off before inserting or removing load plugs