Looking at those instructions for the FTDX10 looks like they are saying to turn on your processor. Under no circumstances use processing, you'll wipe out the waterfall. I have two Yaesu rigs and processing cannot be turned on in the data modes. The FTDX10 is a great rig but they must be using some other method for the data modes.
The method I use was suggested to me by an ARRL OO years ago and that was to run the rig at full power, 100 watts and adjust the power out with the mic gain for the desired output. Doing it that way I would have to boost the mic gain to put out 80 or 90 watts before I showed ALC and start to splash.