Okay Jacques, but just to answer something you asked about, yes some amplifiers do invert polarity, but this would affect all its channels equally, so the connected speakers wouldn't exhibit a wrong polarity issue.

Of course some "audiophiles" imagine that absolute polarity is also necessary, but testing doesn't support such a theory. It isn't unusual for polarity to be reversed several times in the electronics of recording studios.

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Enjoy the music, not the equipment.