Great idea. I too purchaed MultEQ-X after I thought I was so lucky in getting a x3600h before the pandemic completely upended supply chains.
Unfortunately, I more recently upgraded my video to a 4k/8k projector and also obtained a PS5. The price of certified refurbs of the x3800h came way down, so HDMI 2.1 became more of a draw, and I sprung for it.
At least I can still use the x3600h in a secondary room. That room is boomy and vaulted, so at least the MultEQ-X is possibly? doing more than was needed in my theater room.