Hi there,
Thanks for your post and sharing this piece! Always happy to see another Steve Roach fan here.
Do you have an external mixing board? A lot of the dense layers that he creates are done using a mixing console with precise control of reverbs/effects on multiple FX sends. The H90 would work great for this using Dual Mode since you could have 2 different reverbs or other combinations of effects. With the mixing console approach, the background pads/drones can have a lot more reverb applied while the percussion and acoustic instruments can stay more up front. His use of the mixing board is as much of a part of the performance as his sequencers, synths, and other instruments.
Steve has been a big user of Eventide reverbs and other processing effects over the years so you are definitely going in the right direction using an H90. Try some of the Hall reverb presets with a good amount of the high end cutoff, and turn the decay up to the highest setting. Blackhole, Wormhole, and ModEchoVerb would all be good choices to experiment with.
I would highly suggest reading this TapeOp article where he takes a pretty deep dive into his practice including gear and techniques: https://tapeop.com/interviews/161/steve-roach
