Its been mentioned many times to have the digital components on their own dedicated line.... Why is it recommended not to share the same AC line as analogue components?The most significant generators of electrical noise in most systems are components containing substantial amounts of digital circuitry, and power amplifiers. Some of that noise will be fed back into the power cord of the component which generates it, from where it will to some degree propagate through the power wiring to analog components, with unpredictable but potentially perceptible adverse sonic effects.
Everything else being equal, the longer the wiring path is between the power cords of noise generating components and components that may be susceptible to that noise, the more that noise will be attenuated. The most significant reason for that perhaps being the inductance of the wiring. The inductance of wiring is proportional to length. A given amount of inductance presents an impedance which is proportional to frequency. Electrical noise generated by digital circuitry tends to be at very high frequencies, and therefore can be significantly attenuated by the inductance of a substantial length of wire.
Secondly, is a surge protector using isolated receptacles an alternative?It's certainly an alternative to consider and/or try, and in fact that's what I do with my CDP, which is the one digital component in my system. How that approach would compare with having a digital component on a separate dedicated line can't be predicted with any certainty, as it would depend on many unpredictable and unknown variables, including the technical characteristics of the noise generated by the particular digital component, how the particular analog components would react to that noise, the characteristics of the filtering that is provided between receptacles, and the susceptibility of the particular components to ground loop issues if they were to be put on separate dedicated lines.
Best regards,
-- Al