The other thought that might relate to graininess is the printer resolution. You need to make sure it is set to 2880 in the QTR print driver—that can make something grainy and have a lower ink load for the same limit. I have make negatives on a 9900 with my QuickCurve system at a local university and didn't get graininess when using the PK, LK, and LLK inks, but haven't tried it with the P9000 I have access to now.
The second big problem is the ink limits and overlaps that worked for the 3880 are going to be much different for the P7000/9000 so you can't use one set of inputs from one line to another. The inks are different (denser blacks for the same limits) and the head is different from the 3880 to the larger format printers. If you wanted to go through the Ron Reeder method then you would need to start from scratch.
A better way that might get you back up and running faster is to use my QuickCurve-DN system: https://www.bwmastery.com/quadtoneprofiler-digital-negatives/ The starter curves have a much different shape that allows them to be compatible with both lines of printers and has a simple ink limiting and linearization built in. You might never need to use an ink descriptor file ever again...