Zub, welcome. You may have it a bit backwards; the 16ga is ok( study this excellent article and wire table by a well-respected veteran audio professional)but the unfortunate part may have been spending too much on monster, which is as good as the rest, but is overpriced. Don't worry; the 16 ga is fine for the QS8s and you don't need heavier wire for the other speakers either.

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Enjoy the music, not the equipment.