Edibility of quad curves: there have been a number of threads over the last few years that have gone into this, and a few people have worked it out with different kinds of spreadsheet methods. All of that was not for the feign o heart and was before Roy released the linearize-quad app. That works well for a lot of users, and is the first thing that should be used.
All that being said, for the past few weeks I have been working on a way of taking the individual quad curves for a linearized profile and parsing them into 21 steps so I can manually adjust the shape of the ink curves in Excel or Photoshop to get smoother shoulders and long trailing edges (while still maintaining the same ink load). I then put them back into an new ink descriptor file as Curve_ink="0;0 5;25 ... 100,0 " or ACV curves made with PS (and then change the limits to 100 for each of the inks used so the ink load in each of the curve stays the same), and then using my own linearization tools to fine tune the final linearization. I have all that figured out for inkjet positives on paper, but doing the same for digital negatives is what has me hung up now (well, 21 steps is easy, but refining with 51 to 218 steps is a little messy still with digital negatives).
Hope that doesn't muddy the waters too much
Richard Boutwell