Digital BW, The Print

I have used the Cone NK7 inks in an R800 now for some time and haven't 
felt a lack of dmax in my prints except when compared side by side with 
a similar print using MIS Eboni on the same (matt) paper.  The 
smoothness of this inkset has more than made up for this for most 
images though.  Now, however, I would like to try to improve the dmax 
if that is possible.  I use QTR for this printer/inks with the standard 
Cone curves and generally use either Bradford Rag or HM Photorag papers.

Does anyone have any ideas about the best way to do this?  I have seen 
comments about "underprinting" on the site.  Presumably this means 
laying down two inks at the same time on the paper to increase the 
density?  If so is this a sensible approach to take using say the black 
and the next darkest tone?  Would the paper take the additional ink 
load?  Clearly I would have to make my own curves and set the ink 
limits carefully.

Thanks for any thoughts you might have.

David Whistance