cDNA generally does not concern unique splicings. For the most part creation of cDNA is a blind, undirected (by the researcher) process. Standard cDNA is 100% implied by the mRNA, which the researcher has zero control over.

I'm going to assume phonograph=genome, song=BRCA gene, chord=mutation. What is the diamond stylus and laser pickup? Are these techniques for conversion of the song/gene into a scientifically useful format?

If so, it sounds to me like you misunderstand this case. It doesn't pertain to the methods with which one would analyze BRCA scientifically--these have been around for decades and as far as I know have not been patented. It's a question of whether a) the "song" itself is patentable (SCOTUS says no), and whether a derived substance based on this song is patentable (SCOTUS says yes, since nature didn't make it.)

The Court correctly identified that Myriad is not patenting a specific molecule--but rather the information contained within. It is not even a specific nucleotide sequence that is at stake--codon degeneracy and of course medically significant mutations within the BRCA gene necessitate some ambiguity in the specific of DNA sequence for the patent.

The Myriad claim has nothing to do with the creation of BRCA cDNA. They were not the first to perform reverse transcription (and as Thomas notes, Myriad makes no method claims). Nor were they the first to synthesize the cDNA. Anybody who has ever created a cDNA library (thousands of people, both before and after Myriad) have done so. What their patent concerns is the sequence, i.e., the information contained within the cDNA--which is 100% determined by nature.

The latter part of your statement belies the inherent awkwardness of the "chemical not found in nature" argument. When a researcher makes cDNA from mRNA, is the result only "not found in nature" if the original genomic DNA had introns.

So as a result should all prokaryote-derived cDNA be unpatentable? Perhaps only certain cDNA from humans are patentable (from genes with introns)?

Great analogy. Might I add a direct quote from Thomas' opinion: "[Myriad's] claim is concerned primarily with the information contained in the genetic sequence, not with the specific chemical composition of a particular molecule." Pretty much saying the code matters, not the encoding.