There is no difference in the way the dots are laid down? Different print engines though if I am not mistaken, QTR based on the Gimp-print routines versus the Epson 3880 driver that must be more recent.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots