Hi,

The H90 does not offer a mono in / stereo out insert, so I’d recommend using the Dual Mode setup since the Kemper doesn’t have a stereo input.

Dual Mode will give you a proper mono path for your pre effect and a stereo path for the post effects.

Or, if you’d like to use insert mode, just connect 1 output of the Kemper and use it as a mono insert in the H90’s path (not sure if the stereo output of the Kemper is important for your setup).