The vertical is the voltage measured, the horizontal is frequency, so you can see the VMS has a slight high frequency drop off. I haven't calculated what it would be in db, but a slight EQ might bring that up.
I have a signal generator that I set the output as close to 0.775 volts as I could. 0.775 volts is 0dbu, which is represented by the red line.
I then fed this into each of the 3 mixers and measured the output on the XLR outputs across the frequency spectrum from 60hz to 20khz.
The VMS testing was done using an analog channel, I'll do another measurement using a ripped test tone running through Virtual DJ, but I expect to see the same results. As long as the meter on the mixer says 0db, the output should be close to 0.775 volts... not 0.210 volts.