Digital BW, The Print

Hi everbody, 

I recently took the plunge and installed the MIS UT2 B/W continuous 
feed ink set up on an Epson Stylus 1280. I have Photoshop Elements 5.

I've been printing some of my B/W shots using the print driver 
sliders to lightly adjust overall cast (no curves or anything fancy 
yet). I have been very impressed with the highlights and midtones, 
but am baffled by the shadows. They are tending to come out oddly 
light, but with somewhat posterized bits that are very dark in the 
darkest areas. The gentle graduation of dark to darker is replaced by 
gentle graduation of somewhat dark punctuated by black here and 
there. To my eye, it looks like the point at which the grey inks 
leave off and the Eboni takes over is not correct. They grey inks 
seem to be handling too much of the tonal range.

I have no idea how to troubleshoot with this set up. Is this the sort 
of thing that curves woul help with? Although it doesn't seem like 
the sort of thing that would be affected by poor calibration, I have 
not calibrated my monitor - would that contribute? 

I appreciate any/all