Most of the algorithms have some form of EQ (Filter, High Level, Low Level, or similar).  A Series or Parallel routing will also matter on where you target that harshness.  If you hitting the front end with that analog octaver or overdrive, you may have to dial back some of that even before the input.

Nice high end ‘board.  I think it will help to consider each pedal as one component of a large modular setup, gain-staging at every point in the chain.

You mentioned Shimmer, so there’s one thing we can break down.  There’s the overall Decay, plus the breakdown into Low Band-Mid Band-High Band Decay.  Great place to start.  Keep some focus on the Pitch Decay, too.  The pitch-shifting loops around and gets shifted again.  That can contribute to some harshness as loads up on higher / lower frequencies.

Here’s an earlier discussion on Shimmer with the H9 that still applies:  https://www.eventideaudio.com/forums/topic/h9-shimmer-pitch-decay-etc/

It’s a deep pedal, but I think you’ll find you can wring most any result you’re after from inside the H90. It’ll take a few runs through the algorithm selection.  Pay special attention to any differences between algos of the same ‘class’.  Often two algos (say, reverbs) may look like they perform identical functions.  But there’s one or two parameters unique to them that makes all the difference.

Let us know how your progression unfolds.  There is some investment involved, but it’ll be time well spent.