I asked Jon to explain this, and here's what he said:
Our curves actually will produce tens of thousands of gray levels whether the image file is in 8 bit or 16 bit mode - by virtue of how we construct the back slope of each of the curve components and because there are so many shades of ink. Anyone gets the benefit of K6 and K7 when they use the curves that WE construct. While EDITing the image is critical to remain in 16bit - there is no reason not to convert to 8bit only for print - but 8bit can not be converted to 16bit and still not have only 256 gray levels. So only convert for print, retaining the original file for re-editing and archiving. Having said that - only a few of our customers have said that they can tell the difference between 16 and 8 bit files when they tested - but the differences are very minute.
I hope this helps.
Best regards and happy printing~ Dana