Digital BW, The Print

I am using the above combination with Paul Roark's curves, but I am 
getting a non-linear greyscale. When I print the scale, between 40 to 
80% grey there is no evolution, and there is a jump just before 
(around 30%) and after (around 90%). I think this is called macro 
banding. The prints of actual photos show the corresponding shart 
transition from a flat midgrey to white and dark values, making the 
print look very "digital". I think I have all the parameters well 
set, though my software is mostly in French so sometimes it is not 
easy to get the options correctly set in the print menu. The only 
option I can't find in the Color settings, where there is 
no "embedded 4 colours" or something like that and instead I 
have "embedded 5 colours". I have tried different colour settings, 
different paper options, speeds, etc. It is curious that I get 
relatively linear transitions without applying the curves and 
printing directly after having transformed the image from greyscale 
to RGB, but still it is not perfect. I have played as well with 
transfer functions in the print menu, but I am not sure of what I am 
doing and it is not recommended. The inks are charged in the right 
order, I am pretty sure (unless there is a mistake from MIS in naming 
the bottles) Any suggestions of what to try? Should I twickle the 
sliders, transfer functions? Thank you in advance. 
Miguel