Hello,

The H90 has 2 mono insert paths. You can use whatever effects processors you like in either of those paths.

It’s not quite clear to me what your signal chain will be, or how you plan on integrating your audio interface. Please provide some more information if you need help understanding how you will set this up.

An expression pedal can control the input/output gain of the H90, which would work like a volume pedal at the end of your signal chain. Certain volume pedals may also be used as expression pedals, like an Ernie Ball VPJR. If you let me know which volume pedal you plan on using, I can let you know if that will work.

Let me know if you have any other questions.