I would take a look at the “key features” section of the manual here: https://cdn.eventideaudio.com/manuals/h90/1.8.6/content/introduction.html

Almost all of those features are new to the H90 that you will not have with 2 H9s.

Furthermore, we are continuously developing new features/algorithms for the H90, while the H9 is no longer be developed for.

If you can get a good deal on 2 H9s, you can still accomplish a lot, and we continue to support that product, but there are many reasons why the H90 would be an improvement.