Congratulations on getting the printer.
Bart, I tried PhotoZoom, but in side by side comparisons, I can't any difference between uprezzing to 600 dpi (a 1.2 GB file for a 20x30 print) and sending it to the printer at 187.5 dpi and letting the driver so it's thing. Maybe I'm not doing something right.
Thanks for the feedback. Maybe the subject didn't have enough high contrast edges in it? You could also try a larger percentage upsampling to really create a challenge, 400% or more makes it easier to see.
Here is a scanned sample of a 400% upsampled print of the crop presented earlier, printed at 600 PPI, bicubic Smoother (on the left) versus Photozoom Pro (on the right) *
The input images themselves were not additionally sharpened (they were as posted) and both crops were also printed without any output sharpening. The scans were resized to their correct output dimensions on a 96 PPI display. Display size and print size should be identical, although the display is of course lower resolution than the print.
To me, the difference is clear (especially on an actual glossy print), and would be even clearer if a complete output sharpening workflow was used (which was left as an exercise for the readers). As I said, going larger will get even more convincing.
P.S. do download the image and display it at 100% zoom. It seems like the LuLa bulletinboard software downsamples the image for display, thus making the difference less obvious.