QTR-Quadtone RIP

Dear all,

First of all, apologies in advance if this proves to be a stupid 
question !

I run an Epson 2100 and, until now have been using the Epson ink-
set.  Due to my general frustration with getting reasonable b&w 
results, I invested in the Quadtone RIP and Piezography NK7 inks.

My initial prints with this combination (printing onto Epson 
Archival Matt) were good - the tonality and shadow detail were a 
significant improvement on the Epson prints (although there was some 
slight yellow and magenta colour casts  - I guess this may be the 
remnants of the Epson inks being flushed out?).

Yesterday, however, I tried to test how prints from a digital camera 
file would look but had a spectacular failure.  The files 
(originally RAW) were  processed in Photoshop, converted to TIFF 
files, and assigned Gray 2.2 profile.  The prints were, however, 
extremely odd, with most of the mid-tones printing as a blocked up 
shade of grey.  The shadows and higlights seemed unaffected.

As a new user of this system, I was hoping someone might be able to 
shed some light on where I may have gone wrong?

Thanks in advance !

Tom