I'm on the same road as you are, but perhaps a 100 feet ahead. :)
The best way I've found to decode the various sample .qidf files Paul R's provided is to actually read their contents in a text editor. It sounds like you're looking at them already, but in case anyone else is wondering, on a Mac, you can use TextEdit or, if you're a UNIX person, vi or more or cat on the command line. On Windows, do they still have Notepad? You could open it in Word too.
One of the QTR docs (Calibration.pdf maybe?) explains what their contents mean, but they're easy to decode once you know a few things. Let's take a look at STSeb6-Pa325-CK-Yt.qidf.
# at the beginning of the line means the line is ignored. It's there for comments and notes. I put the date, printer settings (eg. 2880u for 2880 DPI, unidirectional), paper, and spectrophotometer I used here for my profiles.
The PRINTER line tells QTR which printer is being used so it knows where the inks are and how to lay them down.
Skip down to N_OF_GRAY_PARTS. In this case, we are using 2 different grey inks, so yes the other grey inks are unused. But, you should still have cartridges with ink loaded in those positions: it's just that this profile doesn't use them.
I've been making two profiles for each paper so far: a black-only (BO) and a 5-ink, and depending on what the image needs --- it's a tradeoff between high midtone smoothness vs. warmth, with BO being more neutral but having ever so slightly crunchier midtones. Depending on the image and paper, I choose one or the other.
The first one (GRAY_INK_1) is in the K (blacK) cartridge position, and has a GRAY_VAL_1 of 100. That's taken by QTR as the blackest ink, because it's 100.
The second ink used (GRAY_INK_2) is in the C (Cyan) cartridge position. It has a GRAY_VAL_2 of 51. This tells QTR to switch over to this ink for tones in GRAY_INK_1 around 51%. IOW, this ink takes over from the blackest ink, when the blackest ink is around 51% This is not a sharp crossover: there is a broad overlap between the two inks.
Further down, we can see N_OF_TONER_PARTS=1, which means we have 1 toner ink. That ink is in the Y position as the next line (TONER_INK_1) shows. Its value is 10, so it will affect very light tones only (top 10% of the blackest ink's tones).
There's more stuff in there, but knowing those things should help you decode what file does what. You can also look at the curves if you find the .quad files and double-click on them: you'll see how the various inks contribute to the final output. The .qidf files get converted into .quad files, which are the actual files QTR uses for figuring out which inks to use.
Good luck, and I hope this wasn't oversimplified!
--Andre