Re: White Paper or Dev Kit for Producing Custom Sample Library?
ARIA uses the SFZ format (or at least some of it) with maybe a few modified commands. I'm no expert.
The book by Simon Cann, "Cakewalk Synthesisers, from presets to power user" (now in its second edition) can be treated as some sort of reference for this. In chapter 13 and the following appendix it lays out most of what you need to know to understand the sfz format. There are also some example files on Simon's web site that can be downloaded.
Then, if you open one of the keyswitch definition files
e.g /Garritan/Personal Orchestra/Instruments/Woodwinds/Flutes/Flute Solo KS.sfz
using Notepad (make a backup copy first or don't alter it without knowing what you're doing) you can examine how the whole thing is structured.
Additionally, if you Google "cakewalk sfz format" you'll find the cakewalk sfz reference material.
I'm aware that there's also a reference to the ARIA player on the Garritan web site which will lead to some more information.
I think this is one of them http://www.plogue.com/category/sfz-file-format/ which will lead you to a Plogue sfz discussion forum.