Hi @martinschki,
- As @Andreas_Haase1 stated, Smart CFX is a Rekordbox specific feature.
- In my personal custom MIDI Mappings, I usually map SHIFT+Headphone Cue to the Neural Mix/EQ Toggle.
a. The MIDI command in djay is called Toggle Neural Mix - EQ and this toggles your controller EQ knobs between regular EQs and Neural Mix EQs. - @Michael_Wisniewski has made a custom FLX4 MIDI Mapping that you might want to check out: DDJ-FLX4 MIDI Map (Unofficial 2.9)
- Also, there is already a feature request topic enable mapping the FLX4 Smart Fader button to the djay CFX Toggle command: DDJ-FLX4 - map Crossfader FX Toggle to Smart Fader button