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Grounding a system is intended to keep every component's ground at the same potential, but in practice this is not possible due to leakage currents, magnetic coupling, etc. so there will always be some current flowing in the ground connections. These currents have no relation to the music signal and are noise, so we want to minimize them. Given Ohm's law, V=IR, reducing R reduces V, which is the voltage of the noise signal in this case. Running multiple lines to your system can increase R quite a bit, the longer the distance from the panel to the system the worse it can get as the grounds are only combined at the panel. So by tying the distributor's grounds together with a low impedance ground cable we can reduce noise and increase resolution, which leads to a better soundstage, more precise imaging, increased clarity and fine detail. Using multiple lines can increase instantaneous current capability, and in some systems it is necessary, but the increase in resistance between component grounds is very often overlooked and unless the system really needs the increased current capability it can often make things worse. Also, there is the possibility that multiple lines could create a huge ground loop, not generally an issue in homes but the possibility can be reduced by running multiple lines together and placing the distributors together. If this isn't the case, which it often is not, then a simple circuit to break ground loops can be inserted with a minor increase in R, which I did with your system since the ground cable was fairly long.
I know a lot of people here have multiple AC lines feeding their system, keep in mind this simple ground modification, I think it can improve a lot of folks' systems! You don't even necessarily need a binding post installed, often a chassis screw will work fine.