I have forwarded another e-mail to HP's support and i am waiting for their answer.
I also talked to some reps here in the States but their answer was mostly ignorance in this matter.
However the review on the LL site also makes mention of this plug -in specifying that details are still sketchy.
i will post HP's answer upon receipt.
It's a bit confusing questions about bit depth.
Now there are two distinct topics around 16 bit images. The images are sent from Photoshop in 15 bit plus 1 padded to an expanse of 16 bit data per channel.
The printer driver or printer itself in Epson's case has to screen the pixel data through masking. The levels and scalability in the masking is where the magic will probably do more magic than the actual number of color levels per pixel.
You can send 8 or 16 bit to the Z without a hiccup, but it's not going to use the data at that bit depth, it's going to scale the data downwards.
So the difference you see with the 16 bit Canon plug in is sending the image pixel data at 16 bit (padded) yet the screens are in the best case 10-12 bits. This does make a advantageous difference for transitions nonetheless.
On the humble 9180 it is indeed 16 bit screening ( the first in any OEM driver I know of) at 4800 dpi.
The Z is not with the driver, and not with the plug in. It accepts 16 bit images but scales. The screens are 8 bit. The plug in codeveloped by HP and Adobe is a convenience tool that doesn't change the driver data stream architecture.
I didn't know the Windows plug-in was not yet available.
It is for Mac but I can't use it with the current 9180 plug-in due to an incompatibility ( that has been fixed BTW but is not public).
Your best option for the Z printer will be to use Colorbyte's ImagePrint. The program runs full 16 bit image depth and high bit screens ( I'd have to check with John at Colorbyte if it is still 12 bit or more).