You must learn to separate individual spot colors into vector images instead of depending on four color process for reproduction, then outputting them to Postscript printers to make positives for screen making.
If you have 6 heads on a press, that usually means only six spot colors - until you learn to use ink transparency or halftones to co-mingle opaque spot colors to simulate more colors.
Start by searching for articles on 'separation' at:
ScreenWeb | August 5, 2007 U.S. Screen Print & Inkjet Technology