QTR-Quadtone RIP

Hmmm...  I guess nobody knows much about the DTP-Inkseparation.tiff
file that I'm having trouble with.  So I'll try another approach...

Are there any guidelines or instructions for creating my own custom
inkseparation stepwedge (21-step) for printing in calibration mode? 
From a quick glance at the file, it appears that a series of custom
RGB combinations are used, and that these are somehow translated in
calibration mode to separate ink channels when sent to the printer.

Any help with this is appreciated!

Thanks and regards,
Dave Keasey