Bride of Son of Zen potentiometer question

[gyrene]

On page 8 of the 1997 Audio Electronics paper Nelson Pass wrote,he shows in Table 1 the Parts List for Main Board and it includes five potentiometers...all of which are noted optional.( shown here http://www.passdiy.com/pdf/balzenpre.pdf)

Question is if they are all optional how is the volume being controlled.

P5 is rated at 500 ohms,so would that be a thumbwheel pot as noted to adjust circuit gain? But P5 is the only slot on the board for a pot.

You can see I'm a bit confused.Any help is appreciated.

[Rodeodave]

From page 3:

"P1 and P2 can be used to protect the input from
higher voltage signal sources, or they can be used as volume controls.
P3 and P4 perform attenuation at the output, and can also be used
either as a volume control or simple gain adjustment. P3 and P4
attenuate the output noise of the circuit as well.
P5 allows intrinsic adjustment of the circuit gain without having to match
the potentiometer values, and as shown with a 500 ohm potentiometer,
allows adjustment from about 10 to 20 dB gain."

P5 adjusts the circuit's gain. All other pots are volume.

[Tiroler]

You need two input and two output pots per channel. These are ALPS RK27114 5KDX4 are a nice choice.