There's a thread on the PixelGenius PhotoKit Sharpener site where a few of us are trying to figure out how to use the sharpener, with its highest resolution setting of 480 ppi, to print 600 ppi images thru the Ipf5000 plug-in: http://forums.pixelgenius.com/showthread.php?p=7115#post7115
We understand there's not likely to be a 600 ppi fix by PixelGenius very soon, because the sharpener was Bruce Fraser's inspiration. This is but a small aspect of a much larger loss.
So far I've determined that it doesn't work to sharpen a 300 ppi image at the PKS 300 setting & then up-res afterwards. Others are trying res-ing up first & then using 300 or 480 settings.
Michael, when you made those 2000(!) 11x17 prints last month, did you make any use of the PK Sharpener? If so, how did you set it - or if not, what did you choose for an alternative?
I've been using PK Sharpener Pro since it became available and tried a great many aspects of it. I find the most critical stage for successful operation of this program is at the Capture Sharpen stage. Here it really is important to properly judge whether the image would do best with Wide, Medium, Narrow or Superfine sharpening - that is, most carefully aligning the kind of edge in the image with the choice of edge sharpening in the menu. By examining the image on the monitor at 50% (a recommendation from Bruce Fraser) I find I can get an approximate comparative impression of what to expect from the printer, but Bruce always warned that viewing sharpening effects on a monitor is not reliable.
There is much more latitude with Output sharpening. I almost NEVER resize an image by changing the native resolution. I re-dimension images all the time of course, with resampling turned off, so the PPI changes from one image to another - anywhere upwards of 180 depending on the crop and the print size.
Normally I select the PPI in the Output Sharpen menu that is closest to the PPI of my image - but it may not even be all that close and the results are fine. For example, there is nothing in the Inkjet Output Sharpener menu between 360 and 480 - where the mid-point is 420. If I output sharpen a 420 PPI image at both 360 and 480 and compare them, generally speaking I have a hard time seeing a significant difference on paper. The 480 may be a trifle crisper. So you can use these settings to control very fine adjustments of crispness.
As I look at digital photos in craft shows and other places, I find many people have a tendancy to over-sharpen - when that happens the prints don't look natural any longer.
That is all by way of an approach to using this program, but it leads into your question about 600 PPI. Firstly, have you actually tried and compared sending 600 PPI and 480 PPI of the same image to the printer and compared the results (without Output Sharpening)? I strongly suspect you will have a hard time seeing any obvious improvement from 480 to 600. There has been a general consensus amongst many experts in this field that depending on print size anything between 300 and 480 will be equally good, and it is pointless sending anything more than 480 PPI to an inkjet printer. I believe that is why PixelGenius limited the tool to a maximum of 480 PPI.
Secondly, have you sent 600 and 480 to the printer using the 480 setting? What difference did you see on paper?
By the way, all these comparisons should be done on paper without a loupe and not by looking at images pumped up to 100% on a monitor, because normally we do not enjoy photographs with a magnifying glass - we just look at them - and from a further distance the larger the print. Some people get carried away with discussion of observed differences of quality by looking at pumped-up monitor images or prints through a loupe. None of this tells anything reliable or useful. The only real test is what you see looking at the print in the normal way. I'd be interested to hear of your observations resulting from printed tests of these various settings as suggested above. It may resolve a lot of the issue.