I have managed to make CC 75 attenuate the sound after I have blown... but not to trigger the sound...
Sorry, I missed this part of the question. We need to talk about the basics.
With the Sylphyo we normally play in MIDI world. We can not trigger a tone just by a CC event. We need a note-on event with note number and velocity value to start the note, and we need a note-off event to end the note. The trick for electronic wind instruments is, to take initial velocity but control the loudness of the tone while it sounds, by a stream of CC messages. Traditionally CC#2 but can be anything else.
As Clint suggested, use a monitoring tool to observe the MIDI stream coming from the Sylphyo. Since you are on a Mac, install Midi Monitor, go to preferences and set the controller format to "decimal numbers". During your monitoring use the various filters to narrow the display to the event types you are interested in.
At very short tones you can easily see that the Sylphyo starts with a breath value, then immediately generates a note-on event with the initial value that is stored in the Sylphyo settings. A stream of CC values follows as long as you blow. When the breath value goes down, a note-off event is generated. Basically you could play similar with a keyboard and a fader or pedal, but not as fluently, intuitive and organic as a good wind controller can do it.
I think this gives you an idea about what you have to do to play a synth you do not know yet:
You have to find your initial velocity. For the beginning and for many sounds you can be lazy and set the Sylphyo's velocity a little below maximum. For sensitive sounds you may want to experiment. A quick way in Logic or Mainstage is, to scale the velocity with the MIDI FX plugin "Modifier" before the instrument. Depending on the system you can also look for velocity curves or other scaling options. Setting the velocity in the Sylphyo diffently for particular sounds is the least convenient way and not recommended.
You got to find a good-sounding way to control the loudness. Sometimes the channel fader can be enough, we often did this with wind controllers in former days as we had less options. I think the Sylphyo sends CC#11 for breath by default. In Mainstage you have an "Expression" dial on each channel. I am not sure what it really does, but it reacts by default to CC#11 and may be all you need. If not, look deeper into the synth to find a parameter that does what you want. Volume, Output, Expression, Amp, Global or Main are common labels for such parameters. For the dynamics of your breath, don't forget that the Sylphyo itself offers breath curves. If you use curves in your computer software, set the Sylphyo's breath curve to linear. Otherwise you never know who scales what.