The Epson ABW driver with settings "neutral and dark" and H=0, V=0 gives slightly negative lab b* values while H+3 and V+3 a bit above the line. These measurements are fairly similar to those obtained with my custom neutral QTR curve using all 3 gray inks and LC (light Cyan) + LM (Light Magenta).
Beware that the prints can be very warm even without presence of yellow like when using QTR curves with solely the 3 gray inks. The only evidence of use of yellow I could find is in the article of Gorgio Trucco who posted microscope images.
Since I am not selling prints, I currently consider my prints obtained with the ABW driver and the above settings as a reasonable neutral reference under controlled lighting . They render a bit warmer under most domestic light.