Using the ML10X as I had suggested allows me to free up an additional loop as compared to running the H90 in Dual Mode, because instead of 2 ML10X loops for the H90, I can use one loop + the second audio path on the ML10X (which would otherwise go unused in my mono signal).
I have finally determined that the culprit is the ML10X firmware. I updated the firmware of everything I could at the same time I rewired my board. Today, I reverted to an earlier ML10X firmware and got the intended results.
I did not know whether the issue was with Eventide or Morningstar, but it appears to be the latter, and I am reaching out to Morningstar.
