Hey just got one of these and you CAN control the FX plug with a little mucking around:
Open the SYNTH version of the plug on a midi channel - Monitor to INPUT
Open the FX version of the plug on a Audio channel - Monitor to AUTO
Then open a 2nd MIDI Channel (Monitor to INPUT) and use it to route the midi from the Synth to the FX:
MIDI From (MS20 Synth channel)
Pre FX
MIDI To (Audio Channel with FX Version)
MS-20FX
Hope this helps
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