The idea is to controlled an audio source with a variable pot (for volume control) . The control voltage is in the +5v range (from 0). Is there any component that by receiving from 0 to +5v (or less) can varied its resistance and control an audio source?
There is such a "thing", it's called a digitally controlled potentiometer.
It's not controlled by a voltage but it's relatively easy to use.
Xicor used to produce them, now they are available from Intersil.
You could give that chip a clock signal, say 20 Hz or so, and control
it with a 3 position DPDT switch. Up / 0 / Down
One switch is for the chip enable and the other switch is for up or down.
Thatcorp.com makes many voltage controlled amplifier for audio use.
National.com makes some, like the CLC520. (very fast)
Ti.com VCA610.
Coolaudio.com V2159
Analog devices SSM2022 & SSM2164
Also research “four quadrant multiplier” MC1494