For Photo Rag 308 on the 3800, be sure to:
1. Use Velvet Fine Art for the Media Type, not Archival Matte or Enhanced Matte. The ink load for AM or EM is inappropriate for the HPR paper. Note that VFA is the Media Type recommended by Hahnemuehle and I have verified for myself that it produces the best results.
2. Feed the sheets individually using the Rear Feed. (You will need to use the RF anyways when you select the VFA Media Type.)
3. Make sure to feed with the correct print side, as noted above. You can use the wet finger test: the side that sticks to your finger is the printable side.
4. Set the Color Density slider in the driver to 0. You should not need to decrease it to -20, and if you do, you will get a very weak black and bad color gamut.
5. Set the Platen Gap to Wide in the driver. You can leave the Paper Thickness as its default value of 5 (5 is the default for the VFA Media Type, which is 19 mils thick, the same as HPR308)
6. You can use either 1440 or 2880 dpi.
7. Make sure to let the print dry thoroughly and don't scuff the surface.