Three long dice (3d4)

Lawrence P Kaster, created these three long dice to cast I Ching hexagrams. Two of them are marked (2,2,3,3) the other one is marked (2,3,3,3). Lawrence sells them on Etsy in many variations together with other I Ching related creations.
I don't have them but from the images I feel they are nice to the touch and really pleasant to throw while casting hexagrams.

The method is rather intuitive:

1. Roll the three dices
2. Sum the face values and draw the line according the following table:
   

   6	7	8	9

3. Repeat steps 1-2 other five times drawing the hexagram from bottom to top.

Probabilities

Assuming the first die is the one marked (2,3,3,3)  we have the following possibilities:

 6 = (2+2+2)                                      

9 = (3+3+3)                                      

8 = (2+3+3) or (3+3+2) or (3+2+3)

7 = (2+2+3) or (2+3+2) or (3+2+2)

 that lead to the following probabilities:

Prob(6) = ¹/₄ * ²/₄ * ²/₄ = ⁴/₆₄ = ¹/₁₆
Prob(9) = ³/₄ * ²/₄ * ²/₄ = ¹²/₆₄ = ³/₁₆
Prob(8) = (¹/₄ * ²/₄ * ²/₄) + (³/₄ * ²/₄ * ²/₄) + (³/₄ * ²/₄ * ²/₄) = ²⁸/₆₄ = ⁷/₁₆
Prob(7) = (¹/₄ * ²/₄ * ²/₄) + (¹/₄ * ²/₄ * ²/₄) + (³/₄ * ²/₄ * ²/₄) = ²⁰/₆₄ = ⁵/₁₆
Prob(yin) = Prob(yang) = ¹/₂

which are the same as the yarrow stalk method.

To get the three coins method probablities, the three dice should have all be marked with (2,2,3,3).