Digital BW, The Print

I've installed MIS VM ink carts on a 1280 and tried the Roark 
workflow current on the MIS site, but my prints are coming out 
slightly posterized in the midtones and lacking black. I've had the 
latter problem using the Brandin workflow on an 1160 with MIS 
original quadtones as well. The problem is not in the file: I'm an 
experienced scanner, and one of the images is a professional 
RGB drumscan.

1) lack of black:
I clipped a bit into the black to try to force the printer to use more 
black ink in the deepest shadows, but these areas remain 
unconvincing, and dark areas just turn muddy. I am now 
tweaking the black channel in the transfer function, and that is 
looking promising, but it darkens the image overall. I guess I 
need to reduce the amount of dark gray ink used (cyan position?) 
to offset the increase in black. Am I on the right track here?

2) midtone posterization:
Transitions in the midtones are not smooth. This is particularly 
evident in shadow areas under the chin on a softly lit portrait. 
Transitions from light to dark gray are abrupt, and separation 
within the dark areas is lacking. The lack of black (stubble on the 
chin, for example) makes dark areas look mushy.

These problems crop up with both warm and cool curves, worse 
with the warm, and are not apparent on a calibrated monitor or in 
prints made with Epson color ink or black ink only. I don't 
understand how the Roark and Brandin curves were created, so 
I have no idea how to go about modifying them. So, I'm tweaking 
the transfer function instead. I'm aiming for a look similar to what 
you get with the Epson black ink only, with plenty of pop and a full 
range, but without the dottiness.

Anyone have any suggestion about how to address these two 
issues? Thanks in advance.

Jacques Cornell