Black_Knyght: "Anybody else think that maybe this isn't a Cylon thing, but that someone, something, else is doing this ??? Some as yet unknown third party, perhaps ???"
Of course: the show's writers!
[Spoilers]
Seriously, though, the writers can pretty much make up whatever they want. A Cylon, for example, is supposedly anatomically indistinguishable from a human, yet he can transmit his entire "mind" elsewhere at the instant of death. Sharon/Eight can interface with human computers by sticking a probe up her forearm, but an X-ray apparently wouldn't reveal any connectors. The fact that Baltar has no detectable "chip" in his skull means nothing; Six might have extruded some of her artificial neurons into his brain (e.g. along the optic nerve) and "wired" him that way.
As for Caprica Six, her "Baltar" may be a psychological artifact resulting from a conflict between her programming and her experience. Creating a "mind" more or less as intricate as a human's is an incredibly complicated process; the Cylons may have failed miserably to forsee the consequences of direct interaction with humans. The only remedy may be Ctrl-Alt-Delete.
Incidentally, with Caprica Six and Eight going rogue and maybe contagious, the writers seem to be setting up a basis for peace between the Cylons and humans, and one possible ending for the current series.
Six of Twelve? Eight of Twelve? Why do I get the feeling that Jeri Ryan may guest star on a future Galactica episode?