Congrats on the new H90!
You could try using the H90 in the stereo loop of the Cortex, and then using the dirt pedals in the loop of the H90. That would allow you some flexibility of whether the dirt pedals are before/after the H90.
Otherwise, it sounds like you will need an additional switcher to be able to change where the dirt pedals are in the signal chain. Or you can use the H90 as a mono insert in the Cortex FX Loop 2 as you are doing already.
