QTR-Quadtone RIP

I am trying to match the output of two printers, an Epson 2200 with UT7 
inks and an Epson 7600 with UC inks. Because of the diffferent inks 
matching exactly may not be achievable, but ball park is desired. I 
have printed out 21 steps for each and measured them with my PrintFIX 
Pro spectro and for the 2200 is lighter through most of the range. I 
then tried adjusting the Gamma (1.1, 1.25, 1.5) and Gray curve shadows 
and highlights(from 6 to 10) for the 7600 curve in Curve Creation, but 
the output by eye did not change enough to measure. But when I changed 
the Shadow and Midtone values (-20, -6), the steps lightened and 
approached the densities of the 2200.
My question is, why am I not getting changes by adjusting the Gamma or 
the Shadows & Highlight in the Curve Creation? Are my adjustments too 
small, or is something else going on?