A preamp line section has 4 functions:
1) control volume
2) select an input
3) add any needed gain
4) control the interconnect cable
The two latter functions are not done by passive controls of any sort. That 4th function is also poorly understood, not only by audiophiles but designers too. Often if you have a digital source, you may not need the gain and so a passive might seem attractive. But the interconnect cable will be far more critical with a passive control.
Quite often if a passive is involved, people report a loss of bass impact and overall dynamics as the volume control is reduced in level from full on. This is likely due to the source having some sort of coupling capacitor at its output, which is then in series with the control. Unfortunately, the Red Book specification for CD demands that the output of the CDP or DAC be high, in fact so high that it can clip all known amplifiers if the signal is not somehow reduced. So a volume control is essential.
Now if you don't need the gain, the obvious solution is a buffered volume control. This is essentially a volume control with some sort of follower circuit (either tube or solid state) that has no gain but does isolate the control from the interconnect cable. This allows for vastly reduced coloration due to the interaction of the volume control and the cable.
Since I listen mostly to LPs, a buffered control in my system is insufficient as the extra gain is handy! But if you plan to play only digital the buffered volume control is your best bet if you don't go with an active line section.
