Thanks, Lee, for an important and interesting inquiry.
The big question is whether prototokos should be interpreted as a Greek
term or as the Greek equivalent of Hebrew BEKOR, "firstborn". If the
Greek is decisive, it may be more difficult to decide, since prwtos/prwton
have different meanings and it becomes more complicated when used as a
component in a noun form. Michaelis (Kittel 6:878) says Dibelius found a
comparative use of prwtos in Jn 1.15,30 and 15.18, and also refers to
Blass-Debrunner Pgr 62 (cf 185,1) and Rademecher 2nd ed. 68,70, but
Michaelis rejects this. Ruiz de Pe~a in his valuable TEOLOGIA DE LA
CREACION p72 defends the meaning "born before all creation".
I think it is more likely that the key concept here is BEKOR from Hebrew.
Of 130 uses of prototokis in the Lxx, 111 translate BEKOR and 6 more
translate related terms; BEKOR is almost always translated prototokos.
Michaelis points out that etymologically BEKOR has no relation to "be
born" nor to "be first" (be before) 6:873. Beckwith-Rinngren (DOTT 2:121)
gives the root or key idea as "to rise". This meaning of supremacy or
primacy corresponded to the position of the firstborn in the Hebrew system
of primogeniture, also expressed by BEKOR. The basic idea of BEKOR is
preferred, beloved, highly valued (see Michaelis' comment on 4 Esdr 6:58,
Kittel 6:874 n.20). It was also used as a kind of superlative: "firstborn
of diseases" is a fatal disease, "firstborn of the poor" means "the
poorest of the poor". In Col 1.15 the emphasis is not on pre-existence
but on superiority or primacy. The hoti clause after prototokos explains
the meaning: Christ is Mediator and Lord of all creation. Michaelis
insists that the thought cannot be that the Son is first of the creatures
because He is creator of all creation 6:878. The verses that follow all
emphasize pre-eminence (1.16s). BEKOR was also used as a title for the
Messiah (Strack-Billerbeck 3: 256ss,626,677) will continue...