I have plugged in stereo mode my H90, AFTER my Dream 65, this way it’s as if I was going from the amp (like an actual miked amp cab) to the mixing desk.
In short, the H90 works as a rackmodule inserted into the mixing desk. Then you have to route your H90’s internal signal according with the effect chain you have in mind. At the H90 output I also use a Lelhe stereo P-split to go straight into a mixing desk or actual amps, and avoid phase/groud problems.
This way everithing works fine and smoothly.
My best advice is to have a proper setting of the UAFX that’s the real control point of the rig, meaning it needs a well shaped gainstage to get the best by the whole chain.
Hope this may helps.