Could you explain a little further, though, what parameters of the cable connecting the source component to a passive preamp would interact with the things you mentioned, beyond interaction with the output impedance of the source component that would also occur with an active preamp?For a transformer-based volume control, it's possible that certain combinations of high source impedance and a high-capacitance input cable, that this could affect the transformer's self-resonance point, and maybe the in-band HF transient response. In the case of a potentiometer-type resistive circuit, the only thing I can think of is the fact that the source component will also see the output cable capacitance at the highest volume settings, like above -6dB.
But this is really grasping at straws . . .