"Those who regard this ritual as a mere devise to invoke or banish spirits, are unworthy to possess it.  Properly understood, it is the Medicine of Metals and the Stone of the Wise."

When Crowley speaks alchemy, he usually means sex-magick. 

Star Ruby in Latin is 'Stella Rubea'.  Liber Stellae Rubeae is a veiled sex-magick instruction on how "to arouse the Magical Force within the operator and how to use it to create whatever may be required."

It is my suspicion that the Star Ruby is meant to be the symolic form of Stellae Rubeae, just as Liber HHH is the mental form of Liber IAO.

As I see it, it works like this:

The magician begins with a salutation to the phallus, thus identifying himself with the spiritual/generative power that underlies all things.

He then projects this spiritual-generative force in the form four pentagrams, blasting all that is before him, while vibrating Therion-Babalon/Nuit-Hadit - that is to say, the masculine and feminine principles in their incarnated and eternal aspects, respectively.

He then crystalizes these currents within himself with the NOX signs, raising a paean to the phallic god Pan.

 

This having been accomplished, he attracts to himself (or gives birth to) a universe of spirits: the Iunges, Teletarchai, Daimones, and Chunoches.

Finally, he proclaims the Great Work completed by formulating the pentagram around him and the hexagram above him - 5=6.

Thus he has aroused the Magical(=sexual) Force within himself, and may use it to "create whatever may be required".  Just as the Star Sapphire is a form of sexual theurgy, the Star Ruby would appear to be a rite of (symbolic) sexual thaumaturgy.