A dual potentiometer is the way it's normally done on commercial equipment. Quite often, the potentiometer isn't stacked, but has two tracks.
This isn't an easy thing to do. Using a FET to make a voltage controlled resistor will work to some extent, but is non-linear and will distort the signal somewhat. The gate voltage vs channel resistance of FETs is also difficult to control, so two parts with the same part number, will have different characteristics.
The easiest way to do it is to use a microcontroller, with an ADC to read the voltage on a potentiometer and use it to control the resistance of a digital potentiometer, which actually attenuates the signal. In commercial applications, the potentiometer is often replaced with a rotary encoder, but I prefer potentiometers, because they can be adjusted with the power off and the position of the dial, indicates the volume.