As far as I can tell, the very first mention of the Apep Consortium was in Target: Wastelands. So there is not going to be anything in older books. I think Loose Alliances has most of the info. You may hazard some guess from the role played by Apep-connected characters in Dawn of the Artifacts: Dusk, but that's about it.
I don't remember any source on who could be behind the United Bank of Panama, Jomaku Industries and the Nubian Insurance Company. Actually, Celedyr could be a better guess than Saeder-Krupp for the NIB, considering Celedyr interests in Nubia.
The Darke connection idea probably comes from the last three comments about Apep Consortium President Abd El-Hameed Hassani in Loose Alliances. He has forme Jaguar guards as bodyguards and was a magical consultant on "release status" at the United Bank of Panama until 2058 (which more or less match the date of Darke failure and Oscuro/Darke removal of Aztechnology board). So, yes, it maybe was an attempt from the author to derail the Darke-Oscuro-Solis connection suggested in Corporate Download. Or it was just a suggestion that Hassani was Darke successor. In turn, Corporate Guide would make this a moot point as the Blood mages faction is officially back within Aztechnology canon-wise (it never really went away in most games anyway).