I don't recall him ever saying that.
Both are line level outs and can achievei equal amounts of level of up to +20dbu.
Here is what I know he has said,
"Let me clarify, you shouldn't NEED to turn the output level all the way up and, in general, if you do, then your gain staging is probably suboptimal.
Unity gain mode is a special mode designed for use with the 4CM. When you turn the output levels all the way up whatever you put in you get out (assuming all unity-gain blocks in the chain). If you have an amp block in the chain then you have tons of gain and therefore no longer have unity gain.
Optimal gain staging would be with the level knob around noon. Higher than this and you risk clipping the inputs of the downstream device. With the level knob at full the Axe-Fx II will probably incinerate a Soundblaster or other low-cost stuff. The max level out of the Axe-Fx II is +20 dBu. Most pro gear can easily handle that but lots of gear cannot and the trend in newer gear is towards lower and lower maximum input levels (due to single-ended designs and low-voltage/low-power constraints). In the old days, +20 dBu was routine. Everything could put out and handle +20. Not so much anymore.
For a Strat, near 100% on the input level is not unusual. I run my Strat around there. It has vintage-type pickups."
Also
Everyone listen and listen closely:
"UNITY GAIN IS ONLY FOR WHEN RUNNING FOUR-CABLE METHOD. OTHERWISE, USE THE LEVEL CONTROLS TO CONTROL THE LEVELS. YOU SHOULD NEVER TURN THE LEVEL KNOBS ALL THE WAY UP UNDER NORMAL USE."
And this seems to indicate otherwise:
http://forum.fractalaudio.com/axe-f...-output-level-2-compare-ultra.html#post558751
"The II is unity gain. If you run "dry tracks", which I'm assuming you mean a patch with just shunts, then you'll get the same level out as you put in (assuming Output set to maximum). See the manual for full details.
Reading the manual is essential for getting the most out of the unit."