I’m using the MM to switch presets on the H9 (which is the only midi device connected to the MM). The latency when switching presets is quite present. Is there a way to smooth the transitions from one preset to another / eliminate the gap between presets?
From MM point of view the only options are
- to use cable connection instead of Bluetooth, and
- Minimize the midi cable length.
If that is what you are already doing then I believe the latency comes from H9 itself.
I have no experience with H9 but with HX Stomp the gap between presets is a known issue. I believe the same is true for H9 
With HX Stomp there is no gap or latency with snapshots that work within the already memory loaded preset. Maybe H9 could have some similar option 
Have you checked any H9 forum etc? 
Manual is always a good place to start 
Seems to be a common issue. Adjust spillover settings in the H9, use a foot switch or write support@eventide.com