Digital BW, The Print

I have been using my R220 with the MIS UT-R2 inkset with both Neutral 
and Warm cartridges now for some time but would like to convert to a 
CFS and bulk inks.  As I like to be able to vary the tone of my images 
on an image by image basis (or even occasionally do split tones) I have 
considered using the warm inks in C/LC and the neutral inks in M/LM (or 
vice versa), however what should I put in the yellow spot?  Is this 
approach sensible or should I just go for the UT-3D?  I would drive 
either using QTR (or Bowhaus if it can drive the R220 - I haven't tried 
yet).

Many thanks in advance for your suggestions.

David Whistance