
*** edits after resolution ***
Okay, there is a difference. At 96k, there are only 2 group mixes instead of 3, and only 3 aux mixes instead of 7, and I'm using 8 of the 10 so the mixing tab shows output levels on all my inputs. These are all stereo mixes in case you were counting.
I guess reducing group + aux buses from 10 to 5 in 96k mode makes sense for capacity, but I didn't find that in MOTU's user guide.
I'll try sending all my inputs directly to outputs and mixer inputs for the main mix, which the monitor mix follows, and see if it works. *** Yes, this worked at 96k. My use of group and aux mixes was unnecessary. ***
I'll miss the audio level displays for inputs that I got by sending each pair through its own mix, but there aren't enough mix buses at 96k to do that even with borrowing the reverb bus. *** This is incorrect. The mix inputs do show levels on the mixer tab. My bad. ***