After some studying and imagining, I came to equate the following shapes with the following numbers:
1, tetrahedron (This is represented by the Mind Stone and signifies positive-space building patterns)
2, cuboctahedron (This is symbolically represented by the Mightstone and the Weakstone. The Mightstone represents gravity, the Weakstone, radiaton.)
3, cube (this represents the negative-space building patterns)
4, octahedron (This is represented by Hedron Archive. It introduces an additional degree of dimensionality to the Mind Stone symbolically.)
5, sphere
6, rombicdodecahedron (this is an inverse cube... it also is the sixth platonic solid but only stable in the 4th dimension. Just like the Hedron Archive represents a shift up in positive-space dimensionality building patterns from Mind Stone, this is the equivalent for negative space in terms of a shift up from a cube. An equatorial section of its 4th-dimensional representation produces the equivalent to the Mightstone and the Weakstone in 3-dimensional space, and an equatorial section of that equivalent section can produces either the cube (3) or the tetrahedron (1) equivalents within their 2-dimensional spaces. (I'm using Mightstone and Weakstone metaphorically. Its actual name is the Vector Equilibrium or the Cuboctahedron.)
7, icosahedron (This is represented by Dreamstone Hedron. It has 30 edges, 20 faces and 12 vertices. It's negative-space equivalent is represented by the number 9 and is called the dodecahedron. Like the icosahedron, this negative-space equivalent is a platonic solid and is known to magic players as a 12-sided die. The icosahedron is familiar to magic players as the "20-sided die." Likewise, the tetrahedron is a 4-sided die and the octahedron is a 8-sided die. Both the 4-sided, 6-sided, 8-sided, 20-sided and the 12-sided dies form the 5 platonic solids. (There's a 6th in 4d, but no need to worry about that one for now.)
The unique part about the Icosahedron and the Dodecahedron is that they form inverses of each other. The centerpoints on the faces of one form the vertexes for the other. They're like penguins. They permanently mate.
Icosahedron has 20 sides, 30 edges and 12 vertexes. Dodecahedron has 12 faces, 30 edges and 20 vertexes. They are "mirrors" of each other, or they are reflections of the same common agent in both negative and positive space forms.
8, Truncated Icosahedron - This is the Frankenstein love-child of the dodecahedron and the icosahedron. It has 12 regular pentagonal faces (just like the dodecahedron) and also has 20 regular hexagonal faces (similar to the icosahedron, except they're hexagonal as opposed to triangular) for a total of 32 faces. There are also 60 vertices and 90 edges.
9, Dodecahedron - The Negative space increase in dimensionality beyond the Rombicdodecahdron.
These shifts in dimensionality can be researched on their own by using an AQAL map and there are also philosophers who study and write about them. I got pretty obsessed with learning about them for a while. I liked Jean Gebser's aperspectival view on the cultural dimensionality of magic, (mind stone) mythic (hedron archive) and rational (dreamstone hedron) cultural models. He posited of a 4th stage called aperspectival which is why I started researching the 4th dimension and is why I got interested in the writings of Buckminster Fuller and people like Randall Carlson in the first place. I think this is represented by bitcoin in our timeline.
Other key relation to 9 is the number of artifacts (60) + the number of lands (21) = 81. 8+1=9
The number of non-artifact, non-creature, non-planeswalker spells = 2+2+2=6, and the number of non-commander creatures + planeswalkers = 11+1=12 (1+2=3)
again, 6+3=9
There is also symbolic relevance to the creatures + Tezzeret forming the 12 that surround the one (Garth.) Garth's story-line is from the house of Oor-Tael Magic. It represents the achievement of secret wisdom and mastery of forms.
Ok, I think that is mostly everything about the deck with respect to number 9. Oh, for the spells that are cmc or less, 10+38+51= cmc 99 total. 9+9=18, 1+8=9. or greater=117, 1+1+7=9
99+117=216. Importantly, 216 is twice 108. 108 is the angle of the degree of the pentagon. 5 x 108= 540 (this is 1.5x the # of degrees of a circle. So double this number gives us 3 circles or 1080 degrees.) Symbolically, the number 9 is also symbolized by the 12-faced pentagonal platonic solids when viewed using dream-logic.
Now for a summary of the metaphorical significance: How I see this is that Garth's "One Eye" are actually the 12 eyes of faces of the dodecahedron (representing nine-ness.) I suppose this can loosely be considered to be a metaphor for the "12 surrounding one" which comprises the form of the cuboctahedron (i.e. the Mightstone and the Weakstone.)