Digital BW, The Print

DavidK,

It's not clear if your problem is in (1) reprinting the same image or 
(2) variations between images.

If (1), then I'd do the the paper towel / windex under the print head 
and clean off the ink wiper blade. Both can contaminate the head with 
undesired pigments, cyan & yellow.

If (2), do (1) first. Then I'd use ABW in the epson driver to get the 
desired hue. I assume that you are adding the color layer to a BW stack 
in PS. If not, all bets are off.

Lincoln