Hey Alexei, I got a response from Eric Persing @ Spectrasonics.
Unfortunately, it looks like a chip mod will have to be created by us to fix this issue.
This is back on the drawing board for our engineer to create.
Here are Eric's comments...
[Yeah...the sustain pedal trick won't work with RMX and the Zendrum.
The notes that the Zendrum outputs are actually too short for RMX to respond to. Our solution that we did for the NAMM show was an extremely elaborate Logic Environment that lengthened the MIDI note data on real-time input. Unfortunately, it's not a fix that the average user could handle....pretty tricky to set-up and use.
You had mentioned last year that you were considering adding an adjustable gate time update to the Zendrum software...what's happening with that? That update would solve the RMX problem for sure. All us RMX users would be extremely grateful for that update! :-)
All the best,