Here I am testing a Yamaha M406. It has an adjustable input impedance of 800Ω to 4K with a maximum output load of 600Ω.
The schematic could short out the output if hooked up backwards, but nearly all line level drivers can handle temporary short circuits.
I chose a 10K linear pot because it will not overly load the output and produces a good curve.
Go ahead and play with the controls by clicking the radio buttons in the table. You will see the green line whip around.
The drawing below the table may help you to get going. Be sure to clearly mark the inputs and outputs.
Links:
Attenuator equations
Potentiometer chart
Line Level voltages
