You'll end up with two potentiometers on the same signal chain. You'll then have to configure them for minimal noise and distortion but if a precedingactive circuit with a potentiometer is adding any noise or distortion then you might end up having to set that to a level that is even lower than the CD standard 2volts.
In some cases though it can't be avoided, like using powered speakers with a preamp output from a headphone amp, because then it puts the volume control closerto your hand. In other cases the secondary knob is just a gain knob, like on studio monitors and when you need to set the gain structure between the receiver/processor's volume knob and the gain knobs on the amps in a car audio set-up.
Basically, even if you could tweak it, it's overall a PITA to deal with, and in the situations where they can't be avoided, at least there are benefits. Like volume control within easy reach for nearfield speakers or being able to use separate amps for the tweeters, midwoofers, and sub in a car with a processor.
