I’m used to MPE where you set the Channel to 1 then the controller can choose how many channels of MPE you have. Then for a split you use Ch 16 and select down for the upper split.
On Hapax, the Track Channel setting offers 2.2-2.16 Channel 15.1-15.15. Seems like 2=1 and 15=16, then the second digit is the number of tracks?
To get my setup to work, I seem to have to choose 15.1 for one track and 15.5 for another (in this case using the same USB out). Otherwise I either get no MPE or what sounds like a mess of MIDI cross-talk. Strangely, this set up with 15.1 and 15.5 works with the target synth even though Channel 15 isn’t routed to anything on the synth.
Stranger still, the Device chosen on the Track has to correspond to the MIDI Channel selected for that track on the synth. For example, synth Hapax Device 1 has to be routed to a synth track that listens for MIDI Ch1. If it’s set to Ch 8 or any other MIDI channel the Hapax is not sending, there’s no incoming MIDI. So, the synth seems to be interpreting the Hapax Device as MIDI channel?
My set up right now is below. It works but I honestly don’t know why! 
Can someone help explain this? 
My setup:
HAPAX:
- Linnstrument into Hapax set as global MPE controller
- Hapax Track 1 set as MPE, Out to USB Device, Channel 15.1
- Hapax Track 2 set as MPE, Out to USB Device, Channel 15.15
- USB Cable from USB Device to Synclavier Regen
SYNCLAVIER REGEN:
- 16 Hapax inputs appear in settings as HAPAX MIDI 1-16
- HAPAX MIDI 1 set to On, Is MPE, MPE Routing 1
- HAPAX MIDI 2 set to On, Is MPE, MPE Routing 2
- Synclavier Track 1 set to MIDI Ch 1
- Synclavier Track 2 set to MIDI Ch 2