Alps make an excellent Conductive Plastic tracked Audio Potentiometer. Penny anf Giles in the UK also makes such a device, but very expensive. You could probably not get anything better than this. Digitally controlled stepped attenuators, or pure Digital attenuators relying on A/D and D/A converters with a DSP in between will not come anywhere a very high quality Conductive Plastic tracked analog potentiometer. Carbon tracked potentiometers are something else, they defenitely have a problem at zero crossing, as does carbon resistors, particularly at low levels.
