As far as I know, the 2400, 2880 and 3880 all use ever-so-slightly different dithering patterns...I don't know how significantly this affects usage in QTR, though. Profiles built for either would probably be a decent starting point for a digi-neg. But you'll definitely have to do some fine tuning and linearization no matter what your starting point. Since everyone's chemistry and working methods are different. You may want to find Clay Harmon's website and postings here, he may have something for pt/pd that would be a good start, too.
I don't do pt/pd, so I don't really have anything that could help you directly, but I've made this suggestion to others and I'll make it here again...you may want to consider learning how to make digital negatives in QTR from scratch. It's a lot easier to troubleshoot a problem if you understand why everything is the way it is in a profile. And rumor has it that the next release of QTR will have built-in linearization for digital negatives.
Good luck--
Greg