Never said anything about removing lines, you simply don't need to use them.
How does running multiple lines mitigate what you think an amp does to the AC power? Multiple lines are not necessarily isolated from one another. If multiple lines are being fed by the same phase then the only "isolation" is the resistance of the wires and breaker in between the lines, which is negligible. If this is such a big issue then you need a separate phase just for amps, but this will lead to issues as all phases will not have exactly the same ground potential, which will cause noise.
Further, code doesn't allow for combining grounds of different lines/circuits outside the service entrance. So if you DO run multiple lines you must plug a distributor into each line and then use a heavy gauge ground strap to connect the distributors together. Othwewise, you need a subpanel just for the audio system placed as close to the audio system as possible, and by adding a whole nother panel and breakers, you're adding complexity and expense and potantially making the sound worse vs running one simple line from the service entrance to the one receptacle near the audio system that has one distributor plugged into it. Simpler is better unless you really need the complexity to achieve a goal. For a simple 2ch audio system there is no need. For a big HT system, sure, you need the capacity to run a ton of high powered amps.
There certainly is a difference between grounding at a panel vs at a distributor, and the longer the distance in between the distributor and audio system subpanel or service entrance, the larger the difference. Noise voltage is directly dependent on resistance by ohm's law, V=IR. You want your grond connection to be as low in resistance as possible, that's why some people and almost all recording studios use heavy gauge grounding or even a copper buss bar to ground their equipment. This is especially true in a single ended system where components IEC inlet grounds are not isolated from chassis/signal grounds.
Bottom line, lower ground resistance is better than higher and you can achieve that while avoiding other potential issues by not going nuts with running multiple lines in a a system that doesn't draw much power.