According to what apalazzolo said…
You could try another solution that’s having one amp sim stereo plugged in front of your H90, then the second amp sim stereo plugged into the H90 inserts. This way it can work as if the two amp sims are stacked together. You now have the chance to have one, the other or both in series, the thing you have to chose is which one goes first, as you can’t swap the two.
Bye!
