Now what about PS, LR, Qimage? How do these applications actually handle the printer color profile conversion of a 16-bit image before sending it to the printer driver?
Can't tell you how Qimage does it, but if you are printing a 16 bit image using either Photoshop or Lightroom to manage color
AND you use the Adobe ACE CMM, then the application does a color transform from the current color space to the output color space (the printer profile) in 20-bit precision. So, while the print pipeline can only handle 8 bit (except for Epson on the Mac or the Canon export plug-in) that final conversion from the image color space to the printer color space has 20-bit precision before the final 8-bit conversion...
Which is one reason that comparing printing in 16-bit is hard to compare to 8-bit. In essence, on Mac or Windows the print pipeline can already handle the 16-bit to 8-bit in high precision. So, it's hard to prove that printing in 16-bit is superior...
In point of fact, the only time I've ever seen a real advantage is when print long and subtle synthetic gradations...Illustrator or InDesign gradations can show better/smoother gradations when printed using a 16-bit print pipeline.
Personally, I'm pretty much on the fence about image detail in a 16-bit vs 8-bit print pipeline. Since I'm using 16-bit ProPhoto RGB images and printing primarily using Lightroom, I go ahead and print using the 16-bit print option. But, I'm using LR manages color and get the benefit of 20-bit precision anyway...but if I forget and print using the normal Epson 8-bit pipeline, I'm not seeing any substantial differences.
If you are printing 16-bit using an Epson on Mac (or using the Canon export plug-in) you may as well use the 16-bit option. The only downside is slightly slower print spooling times...
But if you are printing on Windows using an Adobe app managing colors, the differences will be so subtle as to be irrelevant.
Yes, it would be useful if both OSs offered 16-bit print pipelines...on Windows Photoshop has the ability to use a 16-bit display pipeline (don't ask me why Apple has failed to offer 16-bit).