1: With the small format 1.5 pl printers the first and last 1" or the page are unsuable because, as Roy and others have said, the dithering and micro weaving needed where the paper stays "in place" under the print head is different from when it is passing through the printer. This ink firing pattern is built into the Epson driver on the computer on the smaller desktop printers and not into QTR. There are some complicated controls going on behind the scenes to control what nozzle is firing in what order... The larger format printers like the 3800 and up have that weaving function built into the firmware of the printer and you can print right up to the edge of the paper with no micro banding (i think the 2880 might be free of the micro banding as well, but don't quote me on that).
2: The kind of banding that I was referring to shows up in smooth gradients as horizontal bands where the inks from one shade overlap the inks of the other shades. This is the banding that can be hidden with the additional inks in the toner sections of the ink descriptor file. I have done this using a different color than the main color of the inkset, like a 4 or 5 carbon profile with two shades of selenium as a toner.
This kind of banding comes from how QTR uses a partitioning function based on the cross over points of each ink (the relative dmax for each shade of gray where it intersects on the K curve). If these cross over points are not set accurately or if there is not enough overlap built in from one shade to the next there will be noticeable places there are flat spots or small reversals in smooth gradients. With 4-7 ink profiles I do not consider whole numbers or estimates between the 5% steps to be accurate enough.
I am not sure if using all 8 inks with carbon provides any advantage over a well made 6 gray carbon profile. I can see where it might be better to hide the dots with more inks and lower ink limits, but with the inks as dilute as they are, you will be hard pressed to see any dot when using more than 4 black/gray inks. I think the best option for utilizing all 8 channels would be to made a dual quad printer and blend the two profiles at print time using QTRs multiple curve printing option.
As for the benefit of making your own QTR profiles with the Cone inks: I personally think the Cone carbon has a better color dilution than the Eboni Carbon inks—I know other people feel differently, but that comes down to personal preference. I prefer Jons way of partitioning the inks starting with bezier curves, but it does require using his gray dilution percentages to work properly. I also like that I can more or less swap out one tint to the next without the prints changing drastically. If the Peizography inks and profiles are working properly then I don't see an advantage of making your own QTR profiles with those inks. The shade 7-4 ink curves are much better with Piezography than with the increased overlap settings when made with the QTR tools. The QTR workflow is definitely more demanding, but can be just as good. It is only when Piezography don't work correctly that it is nice to be able to take over and continue to make equally beautiful prints.
Richard Boutwell