Thanks for the comments, guys.
Please note that the measurements I published on AV Nirvana are not as accurate as could be, and are for comparison purposes. The Outlaw support group has taken me to task for this, and I will be correcting my post.
Most notably, the MOTU M-2 definitely has rising THD below about 40 Hz. This is clearly seen in all the sweeps, on other equipment as well.

I'll run some more measurements with balanced output and revise.

How audible is it? Well, if I play the audiophile standard Spanish Harlem from Chesky, the bass notes at the beginning are clearly buzzing slightly (as if the speakers were being slightly overloaded.) This is over speakers and from the headphone jack as well. It isn't audible as noise without signal and higher frequencies are not affected. Test tones below say 200 Hz are also audibly affected. Does it reflect the difference in the 2 sweeps with EQ on and off? EQ on shows a hump in THD between 40 and 200 Hz, but still that's only around .02% at 100Hz... doesn't seem reasonable.

We now have 2 parties who can't reproduce what I'm hearing, so I will post a before/after recording of the output.
I'm just trying to avoid the expense and bother of sending the unit to Outlaw to be told it's functioning ok.
Thanks again
Phil