Out of curiosity: how do you know that / how can you tell?
A few months ago I tested the Pro1000 on Win 10 x64 using PSP and XPS as well as just the XPS driver directly. It prints 8 bits per channel.
Version of PSP is 2.2.3
How to tell for sure:
1. Using Excel or a text editor, Create a patch set with the following RGB values:
[220.00 220.00 220.00]
[220.33 220.33 220.33]
[220.67 220.67 220.67]
[221.00 221.00 221.00]
[221.33 221.33 221.33]
[221.67 221.67 221.67]
[222.00 222.00 222.00]
2. Duplicate it at least 10 times
3. Import it into Patchtool and generate a 16 bit tif image profiling target for I1Pro 2
4. Assign it to ProPhoto RGB or just keep unmanaged.
5. Scan it in and save the scan as a CGATs file
Load it in excel and sort the rgb values so the duplicates are all grouped. Average each group and plot the L*
A 16 bit print path will plot the L* values along a fairly straight line
A 8 bit patch will stairstep every 3 groups.
Here's what a failure looks like:
And here's a workaround. Use the 8 bit dither option in Photoshop on 16 bit tif tiles. The next plot is from my Epson 9800 using the standard 8 bit driver.