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There is not much available in 16" tires. Best bet is to move up to 17's like the WS6 coupes came with (17x9.0" 50mm offset).
Even some of the 17" tires are getting harder to find in the recommended sizes.
For same size wheel/tire on all four corners, 17x9.5" with an offset in the range of 45-56mm will work. Run 275/40-17 tires, and the outside diameter will match your current tires, so no problems with speedometer/odometer calibration.
For a wider wheel in the back, consider a 17x10.5" 45-55mm offset, or 17x11.0" 45-50mm offset wheel. The 11" wide wheel can cause interferences on the inner side of the wheel/tire, and places the outside edge of a 315/35-17 tire just under the outer edge of the fender, looking straight down from above. You could fit the same tire on the 10.5" wide 50mm offset wheel with no issues.
You can also use an 18" wheel, same offsets and widths mentioned above. Tire size would be 285/35-18 for the 9.5" wide wheel, and the same of a 305/35-18 on the wider wheels.
I'll add some pictures in the next post.