In his comment for the King of Pentacles, Waite wrote, "The sign of this suit is represented throughout as engraved or blazoned with the pentagram, typifying the correspondence of the four elements in human nature and that by which they may be governed." I believe "that by which they may be governed" refers to mind. The pentagram represents mind (on top) over matter (four points below). In The Devil we see the opposite situation in the reversed pentagram. In his chapter on the pentagram in Transcendental Magic, Lévi wrote, "The Pentagram signifies the domination of the mind over the elements..."
I'm not very familiar with the GD's symbolism in this suit, but the winged cross on the Ace might express a similar idea of mind over matter.
By hexagrams do you mean the King of Pentacles' scepter? I don't really see any other hexagrams unless I'm missing them.