What method of interpolation do the printer driver and 16-bit Photoshop Export Plug-in use?
Both the printer driver and the printer itself use nearest neighbor interpolation (the least accurate). The 16 bit Photoshop Export plugin defaults to nearest neighbor, but can also be set to bilinear or bicubic on the Main tab by choosing Set Configuration. Preferred method of interpolation for best quality when upsizing is to bicubic.