I tried it two ways:
stereo 1/8" out to stereo mic in. Looked okay, but with some feedback at the top end.
Mono, 1/4" plug channel 2 out to in. Looked great. Mostly flat with a slight roll off on each end. That seemed to work best for me.
The XLR mic is fine with the phantom power. I upped the reference sound to 78dB and get -12dB on the input channel during level setting. Sweeps look good so far.
At 75dB and full gain on the input channel, I was getting just below -18dB and the error message, but so far things seem to work. When in doubt, trial and error
Thanks for the input, guys.